Twitter user @antman8o8 took this photo while leaving Comic-Con and it appears to be an Ultron Drone from Avengers: Age of Ultron. Obviously the Drones and Ultron will be CGI so this is probably used to reference lighting while on set. If you haven't see the full poster of Ultron Drones fighting the Avengers, make sure to check it out. Via Nailbiter111 at CBM.
Avengers: Age of Ultron will become sentient May 1st, 2015 (USA).