Are those just TM Tracer units?
some of them are and the rest look liek they could be these
i dunno if it could be the mags...the light that charges the bb would be coming from inside the mag and i'm not so sure you'd be able to to see it all the way down the barrel. Plus, some of those flashes were bright red and the light from a tracer unit is white.
What's a signature?
The LED in the G&P mags are constant on/off and held below the lip so in all probability not. As for simulating muzzle flash, google it, I believe someone has made one with schematics.
Pygmy Militia Group