The lights are on
Some cosplayers spend weeks or months crafting their outfits down to the most minute detail. A hero's sword can be replicated from plastic, or foam, or some other material that takes honest skill to hone into a believable prop. Sometimes, cosplayers just grab a real weapon.
Destructoid's Dale North reports that he heard Comic-Con security guards joking about how many of the fake weapons used by cosplayers look genuine. The reporter also discovered that replicas simply will not do for some hardcore (lazy?) cosplayers, and genuine weapons have been carried to the convention. Allegedly on the first day of Comic-Con one attendee showed up with an AR-15, which you're probably familiar with from video games.
California news outlet Sign on San Diego says the security crew seized two machetes, a dagger, a commando-style K-bar knife, and a lead pipe. I'm assuming the latter of the weapons belonged to a Mike Haggar cosplayer.