>>>>>i say put a universal sign that warns (something to the effect) "are you stealing a bait bike"...get them psychologically<<<<

When I used to speak to jewelry salesmen about the GPS issue, I would suggest that they purchase and utilize a piece of equipment called a GPS Jammer, which would squash any signal transmitted by a GPS tracker secretly attached to their vehicle and make them invisible to anyone trying to follow them. If, as someone else mentioned, many bike thieves are "professionals," they will catch on to the bait bike idea pretty quickly and will simply carry their own GPS Jammers to keep the cops away.