> Actually the rule is that the merchant can ask me to sign the card and ask for valid id which I showed her

You sure about that?

> Not at the post office.

> “It is a policy that it must be signed when presented at retail counters,” said Lisa Gamboa, consumer affairs manager for the U.S. Postal Service’s Colorado and Wyoming district. “It’s a security thing to prevent any potential fraudulent use and the card companies have it in our agreements with them.

https://www.denverpost.com/2007/09/02/see-id-dont-do-it

You should tell the post office what’s in their agreement. I know a Karen and it is you.