I live in Washington state. I tried that same thing, and sure, many merchants don’t even bother looking or pay attention. Very few do. Not very long ago, the Washington State Liquor Stores (they are state run, unfortunately), absolutely requires to have a signature on the card. I think this may be a state requirement. So you may not be able to put “see ID” on the sig line on the back.

A second comment, I had a discussion with one merchant who informed me that if someone uses the swipe machine, either for debit OR credit, that they cannot be required to check for ID. I don’t know for sure if this is correct for credit cards (it may only be debit), but I’m sure it was something that came out of the credit card lobby, or at least the companies that are making the machines. This refers to the machines at checkout lines as much as the automated ones at gas stations.