So, I've been going to my boss's bank to cash my check with the stamp on the back. Been doing this since the original date of this thread. This past Monday, 12/4/17, I sat in the drive through for 30 minutes while the teller (who'd never seen my check stamp) obviously asked a superior about the stamp.

Teller: Sorry it's taking so long. We're checking on the endorsement on the back. "They" want me to ask you if your employer has asked you to use the stamp.
Me: No
Teller: Why are you using the stamp?
Me: It has to do with Federal Reserve and filing taxes
Teller: OK

She cashed it.

I have a question. I assume the bank has a legal obligation to cash my check that came from them (stamp or not). Does anyone know for sure on their legal obligation on cashing their own checks? I do not have an account with them