You don't need to add which fandom you're from. You don't get points for liking something from another group, even if that group is your "rival". You're not special for being in one fandom but liking something from another group it happens all the time.
People who write "I'm a (fandom) but I'm here to support (other group)" or "I'm (fandom) but this group are really amazing live." just sound desperate to be special. No one cares which fandom your from.