Nobody looks at credit card signatures. (Vectored in alt.fan.cecil-adams, by way of Jo.)
My One True Ex writes SEE I D
in the signature strip of her card, and hands over her internal passport non-driving license along with it. Waitresses nearly always hand the NDL back to her at the first opportunity, apparently assuming that she put it on the tray by mistake. Nov 2004: Improvement! These days they usually do look at the NDL.