Dan Reeves was interviewed via phone on "Outside the Lines" on ESPN: According to Reeves he used to have his backup QB try and figure out defensive signals while on the sidelines, and one of his QB's was particularly good at this and usually by half time he'd have their defensive signals figured out. Reeves claims that really what it helps for is Blitz pickups, but it doesn't always work in game since teams can change their signals. He said a long time ago when he played against Mike Shanahan he actually knew all the Broncos signals because they were still using the same signals but they still couldn't stop the Broncos. He said thet where it can have the biggest effect is by adding the info you gained into a folder of information on that team and after time you can start to figure out their tendencies. Reeves said stealing signals itself is very common and every team does it, but he's not aware of other teams using video cameras to do so.