Avoid putting your money in the door pocket. People are going around walking up to taxis from all sides and reaching in through an open window or opening driver doors if they're unlocked, then grabbing moneys.
So avoid making your money too plainly visible especially to the people outside your cab. And it may also be helpful to not roll your windows open enough to let arms reach in when you're at a red light. Lock your driver door, and your other front door. Also give yourself some space before the crosswalk when you stop at a light, so that you have some rolling room if you see somebody walking close to your cab. If they nervously run up to you, while trying not to get your attention, then you might want to wiggle around with the reverse and the drive, or something to freak them out.
I dunno, personally I try not to get to nervous about these kind of things, but be on alert as these criminals are out there.