There was a guy last year who was at another convention and decided to sling his M4 on his back and walk outside. I believe 5 separate 911 calls were made. He was surrounded by cruisers in minutes.
I was at last year's fan expo. There was an airsoft P90 for a Stargate impression and another M4 for a MW2 Ghost impression. If theres the slightest chance that something can go wrong (and in this case there is), its not worth it. It could be scared kids or overprotective parents that can set something off. Seriously, dont do it.
H&K G36c (KWA) / Glock 18c (TM) / Kimber LAPD SWAT Custom (TM) / Mossberg M500 (ACM)