We're told Douglas wore a lucha libre style mask and white t-shirt to the ring. During the Kane vs. Big Show match, he ripped off the t-shirt off and revealed a black & yellow "Franchise" shirt. He also ripped off the mask, revealing his identity. Douglas then proceeded to scream a bunch of stuff into the audience so they would notice him. Judging by the video that has leaked online, not many people knew or cared who he was. Several fans did chant "ECW" though.
Douglas fled the ringside area and was escorted out of the building by security following the outburst. Obviously, this is going to generate him a ton of heat with WWE management but I'm guessing he doesn't care.
Once again, here is a video of the incident: