I'm hesitant to say this, but it seems a little self-absorbed and ungrateful for a player at a school signing ceremony to be thinking, 'What's he doing in the picture? He didn't have anything to do with it.' Even if it's true.
A school signing ceremony isn't just about your accomplishments. It's also about proud things that are taking place at the school - which is the one putting on the party. If you really believe that the coach and school had nothing to do with it (which might be entirely true), then decline the invitation to be part of the school ceremony. Just say, 'Sorry, but this has nothing to do with Central High School.' Then have a private signing ceremony and invite who you like. But if you do accept the invitation, then be gracious, IMO. Same for parents.
A school signing ceremony isn't just about your accomplishments. It's also about proud things that are taking place at the school - which is the one putting on the party. If you really believe that the coach and school had nothing to do with it (which might be entirely true), then decline the invitation to be part of the school ceremony. Just say, 'Sorry, but this has nothing to do with Central High School.' Then have a private signing ceremony and invite who you like. But if you do accept the invitation, then be gracious, IMO. Same for parents.