The day this scene was shot, there were 10,000 extras there at Heinz Field. Most of them brought their own props and costumes, so clearly one guy has been smart and, when drawing the 'R' for the 'Rogues' signs (for the Rogues are Gotham's team), he's drawn it in the style of a Robin logo, off his own back. So this is no more a 'clue' that Robin will be in the film than the presence of the Batman logo on a door during Following was a 'clue' that Nolan would one day make a Batman movie.