Buy a Park Pedal Wrench and use velcro ties to afix it to your bag strap (this enhances the pre-beating nervousness of the perp; nothing like seeing a determined cyclist remove an instrument of punishment from their person....almost SWAT-like). When someone walks past your bike (you should be watching from the bar), jump outside and beat them with the pedal wrench (now removed from said strap). Lay the unconscious body across your bike and pin a note to it that says "This will be you if you touch my bike"
That should clear up any theft issues you might have in Philly.
Glad I could help

Or...take the bus