Leave your bike unlocked. Find a nice stakeout across the street, preferably a pub, and wait... Then, if and when appropriate, approach the bastard nicking your bike, kick him in the balls and light him on fire; nothing says "please leave my bike alone you fucking bastard," like kicking the thieving little shit in the groin and burning his sorry arse to hell.
Leave your bike unlocked. Find a nice stakeout across the street, preferably a pub, and wait... Then, if and when appropriate, approach the bastard nicking your bike, kick him in the balls and light him on fire; nothing says "please leave my bike alone you fucking bastard," like kicking the thieving little shit in the groin and burning his sorry arse to hell.