Last week I had lunch with Hardy, a Get Rich Slowly reader here in Portland. We chatted about life (and personal finance) over burgers and fries. He generously offered to pay the bill. When the waitress returned with the credit card slip, she asked to see his driver license.

“What was that all about?” I asked.

“Asking for my ID?” said Hardy. I nodded. He flipped over his credit card and showed it to me. He’d written SEE ID where his signature ought to be.

“Does that work?” I asked.

“Some of the time,” he said. “It gives you an idea of which places are paying attention. But not every place will accept it. It’s technically against the rules because the card has to be signed. Plus, businesses aren’t really allowed to ask to see your ID.”

“What do you do if they refuse to take your card?” I asked.

“I carry a backup,” said Hardy. “This is my main card. My back-up card has my signature, but I rarely have to use it. The only place that I know will refuse the main card every time is the post office. I have to use a signed card there.”

I was intrigued by this attempt to thwart identity theft, so when I got home I asked my Twitter followers:

My lunch companion doesn’t sign credit cards, but writes “SEE ID” on the back instead. Have you ever seen this?

I was shocked by the number of replies. Apparently, I’ve been living under a rock. Over 100 Twitter users replied to share their experiences with this tactic. Here’s what I learned:

  • Though many people write some form of “SEE ID” on their cards, it doesn’t seem to matter. @khaibit2763 writes that only about a quarter of merchants actually check ID. Others write that almost nobody checks.

  • Many tweeters correctly noted that most credit cards clearly state that they are “not valid unless signed”. Technically, writing “SEE ID” invalidates the card and voids the contract with the issuer. Still, not all issuers seem to be aware of this. I found this ID-theft awareness brochure [PDF] from Capital One which notes that one way to protect your cards is to “write that the merchant must check ID on the back of the card”.

  • @lildebbie77 made me laugh with her reply: “When I waited tables I saw it once or twice a month. The craziness? Some people get mad when you ask to see their ID.” If you choose to do this, don’t get upset when people comply with your request!

  • @katekashman uses a slightly different tactic. She leaves the “call to activate” sticker on the card. “Maybe a thief will think it isn’t activated,” she writes. “It isn’t much, but it’s something.”

  • @lizweston noted that this is one of her 9 big credit card myths at MSN Money. In her article, she writes, “You’ll certainly deter use of your card, because merchants aren’t supposed to accept one that’s not signed on the back, and that could affect you as much as any thief.” (Sidenote: Liz will be our guest on The Personal Finance Hour in two weeks!)

  • If you want to cover your bases, consider the advice from @aslaughter: sign the card and write SEE ID. And thank the people who actually ask to see your identification.

So, is writing “SEE ID” instead of signing your credit cards a good idea? It’s hard to say. Technically, it’s against the rules, and few merchants seem to notice, but it gives many folks a warm, fuzzy feeling. Plus, if you’re worried about your card being rejected, you can always do what Hardy does: carry a back-up to use at the Post Office.

Here’s a final word of caution: Jake Billo notes that if you present both your credit card and driver license to a skilled criminal, you’re just giving them more ammunition to destroy your life. He warns that this practice may actually increase your risk of identity theft.

For more tips on protecting your ID, check out my post on how to prevent identity theft. You might also be entertained by the credit-card prank over at Zug. Photo by szlea. If you’d like to help with future GRS posts, follow me on Twitter!