What I love to do sometimes, is at stores where I **know** that they mark my legal $20.00 bills to see if they're "counterfeit", I take out the same marker (one that I own) and mark the bills that the cashier gives me in my change, as I always feel that they're pricks when they do that. You never know as they might be trying to pull off some counterfeit bill in your change. And that marker doesn't really do anything anyways, as good counterfeiters bleach the bills and reprint the different design on the legal paper where the marker is useless, unless if you were to hold the bill up to the light to check to see what president's face is in the "spot" compared the face that's on the face of the bill in actual ink. I feel that if they mark my bills to see if they're counterfeit, I might as well do the same to them to see if their bills are counterfeit.
And since I work as a cashier (as I know the thing about the face that you can see in the light), I let customers slide by with their credit card signatures as whatever they want. I take it as just as long as they marked something down on their receipt that I get to keep, it's fine. In very small print on the bottom of the receipt, it states that upon signing the credit card receipt, you are agreeing to the charge as highlighted above for such goods or services. And by law, each business has to keep credit card records for at least 7 years, in case if there is any discrepencies that might arise with false charges. And at gas stations, you are "digitally signing" for your credit card charge by entering in your ZIP code.
- Mike.