Has anyone heard of a credit card bonus offer specifying that you must be a new member to their rewards program to be able to get the sign up bonus?

As an example, if i'm already an aa advantage rewards member and go to sign up for one of their cards with a bonus, but the terms and conditions specify you must be a new card member and rewards member.

I was looking at some application (don't recall the exact one) and I think I was probably reading the terms and conditions wrong, but wanted to check if anyone with experience could tell me if they had come across it.