The phrase "to sign a shirt" means to write your name or a message on a shirt with a pen or marker as a way of leaving your mark or showing your support. Full definition
The range of prizes available changes, mainly because we try and secure one of a kind football related items, like signed shirts or football club experiences. (oulala.com)
The players also left their shirts behind and Walcott and the ox sign shirts for Sutton players. (justarsenal.com)
SEE MORE: Photos: Gareth Bale gets snubbed after Euro 2016 Premier League promotion - specialist in talks with FA over Three Lions job Picture: David Beckham sends Manchester United starlet signed shirt with encouraging message (caughtoffside.com)