But then again.. it's going to be at the shelter, where people are already coming to, to adopt
Not all people are at shelters to adopt. We had more coming to drop them off than coming to look for one to adopt... I would put something on it along the lines that stated "If enough people spayed and neutered, we wouldn't need places like this! (shortened somehow but how they would get the message.)
Maybe "spay & Neuter = 0 shelters"?