Interesting idea, but you could run afoul of laws requiring visible differences between real and fake guns (namely, fake guns are required by law in most states to be in really funky colors, or marked in some way that clearly denotes them as fake/toys).
And I'm pretty sure that such a claim could get the caller arrested if proven false. Wouldn't that count as a fraudulent report?
If the person makes a claim, and the police find you with a gun it is difficult (without a video of the scene) to prove that you did NOT pull your gun. If there are 2-3 other people making the claim it is even more likely that you will be charged.
That's why I was thinking about concealing a distinct characteristic of the gun. A few minutes with some Krylon and some masking tape should allow me to have a 'third witness' (the cop/jury) to back up my claim that I never pulled it.
TRG