Most of the time our clans check ahead of time to see what restrictions the event has, but at Orthar also states above...we rarely run into this because 90% of our troops are in a "hired" (you hire mercenaries right? =P) status.
I personally have never been tagged at a convention, and I've never been asked by staff to get a weapon tagged at any con (DCon and SDCC included). I only pull my pistols for pics, and rarely carry anything larger than a pistol...so that may have alot to do with it. I don't care for the brightly colored tape on my nice weapons, and don't go out of my way for them to put it on. =P