Sadly he's no longer around to do so, but I wonder if he was okay with signing it. Not that it matters to this conversation, but I can see where someone says "I'm not on it, why would I sign it?"
Also it sets up a bit of a precedent for other captures of just a player name, or reference.
i.e. You can see a teammate's number on a bat being used by the subject, is that player getting a link? No. Or anytime a portion of the scoreboard with the lineup listing captured count towards the player names, or reference to them (uni number and position) you can make out, those players do not count in getting linked to.