Latest / The Copywriting Podcast with Fexingo: Sales Letters, Headlines, and Persuasive Writing / How a Handwritten Underline Boosted Response by 37 Percent
Transcript
- Lucas: Alright, let's talk about a copywriting technique that feels almost too simple to work — but in a controlled split test from 2002, it lifted response by 37 percent. Luna: I've got to hear this. Was it a headline change? A new offer? Lucas: Neither. It was a handwritten underline. A red pen underline under a single sentence in a typed direct mail letter. Luna: Wait — just an underline? No note, no arrow, just a line? Lucas: Just a line. The control was a clean, professionally printed letter. The variant was identical except for one underline — drawn by hand in red ink — under the sentence: 'You can start using the software in under 15 minutes.' That sentence was already in the control. The only difference was that underline. Luna: And that single line lifted response by over a third? Lucas: Exactly. The campaign was for a B2B project management tool, mailed to IT managers at mid-sized companies. The test ran on a list of 40,000 names, split evenly. The control pulled a 2.1 percent response rate. The underlined version pulled 2.88 percent. That's a 37 percent relative lift. Luna: That's massive for such a tiny change. What's the psychology behind it? Lucas: The agency that ran the test — a direct response shop called HBR Group out of Chicago — called it the 'annotation effect.' The idea is that a handwritten mark on a typed document simulates a prior reader. Someone else has already read this letter, and they found something important enough to underline. It's a social proof cue, but more intimate. It says 'this is worth your attention.' Luna: So it's like seeing a highlighted passage in a library book. You think, 'the last person who read this thought this part mattered.' Lucas: Exactly right. And in the context of a sales letter, that implied endorsement — from an anonymous previous reader — can overcome skepticism. The underline also breaks the polished, mass-produced feel of a typed letter. It introduces imperfection, which signals authenticity. Luna: But why red ink specifically? Was that tested too? Lucas: They did test blue and black in a follow-up. Red outperformed both by a significant margin. Their hypothesis — and this is backed by some eye-tracking studies from that era — is that red stands out as corrective or editorial. Teachers use red pens. Editors use red pens. So a red underline carries a subtle 'teacher's approval' or 'editor's pick' connotation. Luna: Interesting. So it's not just any underline — it's the color that adds authority. Lucas: Right. And the placement matters too. They underlined the sentence about ease of use — not the discount, not the guarantee, not the testimonial. The agency's creative director, a guy named Dan, told me they chose that sentence because it addressed the biggest objection: implementation time. IT managers were worried about a long rollout. The underline essentially said 'this is the part you need to believe.' Luna: So you underline the biggest fear-buster, not the biggest benefit. Lucas: Exactly. The benefit — 'you can start in under 15 minutes' — was already stated. The underline directed attention to it and added credibility. And here's the thing — this technique didn't die with direct mail. I see it online all the time now. Luna: How do you replicate a handwritten underline in an email or on a landing page? Lucas: A few ways. One is to use a font that looks like handwriting for the underline effect — but that's tricky because the rest of the copy is typed. The mismatch is what makes it work. Some marketers use a highlighter effect in images: they take a screenshot of a paragraph and add a yellow or pink highlight over the key sentence. That's essentially the same psychology. Luna: Or even a simple underline in a different color, like a red or blue text underline, could work? Lucas: It can, but it loses the 'handwritten' feel. The imperfection is part of the signal. A perfect CSS underline looks like it was designed that way. The whole point is that it looks like someone grabbed a pen and marked it after the letter was printed. Luna: So for digital, you'd need an image of a handwritten underline pasted over text? Lucas: Yes, and some marketers do that. The key is to make it look organic — slightly wavy, not perfectly straight. And the color should contrast with the rest of the page. Red is still the default, but I've seen bright green and even orange work in tests. Luna: I wonder if there's a generational difference. Younger audiences might not have the same association with handwritten marks. Lucas: That's a fair point. I've seen A/B tests on landing pages for a SaaS product targeting Gen Z — they tried a digital 'highlight' effect that mimicked the yellow highlighter tool in PDFs. It outperformed the control by 12 percent. Not as dramatic as the 37 percent lift, but still significant. So the principle holds — it's about simulating a previous reader's attention. Luna: So the format changes, but the psychology stays the same. Lucas: Exactly. And here's another layer: the agency also tested adding a handwritten 'Yes!' in the margin next to the underline. That version actually underperformed the underline alone. The margin note felt too staged, like the writer was trying too hard. Luna: So restraint matters. A single line is more believable than a full annotation. Lucas: Right. The underline is subtle enough that the reader's brain fills in the story: 'Someone else read this and thought this was important.' A full note feels like a sales tactic. The underline feels like an accident, like someone forgot to erase it. Luna: That's fascinating. It's almost like reverse psychology — you want it to look unintentional. Lucas: Exactly. And that's the broader lesson for copywriters today: perfection can be a liability. In a world where every email is templated and every landing page is optimized, a small imperfection — a handwritten underline, a smudge, a slightly crooked line — can be the thing that feels human. Luna: And that human touch is what cuts through the noise. Lucas: Yeah. Look, the reason I dug up this old case study is that I think we've gotten too polished. Every marketing piece is A/B tested, designed by committee, and run through Grammarly. But sometimes the most effective change is the one that looks like a mistake. Luna: It's a good reminder. By the way, speaking of things that keep this show going — a few listeners have asked how we manage to produce this many episodes without ads. Lucas: Yeah, it's a good question. The honest answer is that a small group of listeners chips in monthly through buy me a coffee dot com slash fexingo, and that support is what keeps the podcast ad-free and independent. Luna: It's not a big ask — just that if these deep dives have given you a tactic you've actually used, maybe consider tossing a coffee our way. No pressure either way. Lucas: Right. And we mean that. It's just that listener support is what lets us keep doing episodes like this one, where we can spend half an hour on a single red underline from 2002. Luna: Alright, back to the underline. You mentioned a follow-up test — did they ever try combining the underline with a handwritten note in the PS? Lucas: They did, in a later campaign. And the combo actually hurt response. The PS note alone lifted response by 22 percent. The underline alone lifted it by 37 percent. But together, they only lifted it by 18 percent. The two elements cannibalized each other — too many handwritten marks made the letter look gimmicky. Luna: So you pick one handwritten element per piece. Don't overdo it. Lucas: Exactly. One signal of humanness per communication. More than that, and the reader starts to think 'they're trying to manipulate me.' The underline works because it's a single, almost accidental-seeming cue. Luna: I love that this is a case where less really is more. Lucas: It is. And I think the same principle applies to other formats. In a video ad, a single flubbed word — left in intentionally — can make the speaker seem more authentic. In a podcast, a slight hesitation can signal thoughtfulness. The underline is just the direct mail version of that. Luna: So the takeaway: add one deliberate imperfection to your next marketing piece, and see if it lifts response. Lucas: Test it. But choose the imperfection carefully. Underline the objection-killer, not the headline. And use red if you can. The data from that test is twenty-four years old, but human psychology doesn't change that fast. Luna: I'm going to try this on our next email. Maybe a handwritten underline under the call to action. Lucas: Let me know how it goes. And if it flops, you can always blame it on the 2002 copywriter.