It appears Bungie's viral marketing is being set in motion. With the latest Bungie update theres a quicktime 360 view of the M12 Warthog, IGN points out if you slowly rotate the Warthog to the left, flashes of the following message appear:
IGN points out the 713 number may reference something may happen on July 13, maybe a beta? This would be far after the "Spring" that was promised but we'll have to wait and see. IGN is asking for all your best theory's.