According to a tweet from Matt_Boyd, "Yellow signs for a production named 'E7' off the highway near Raleigh Studios in Pontiac, Michigan." The yellow "E7" signs where used to mark the production locations of the three previous films (pic example from ROTF) so not a leap to assume this is for Transformers 4. Since its still early for principle photography to start, its likely pre-production prep but 2nd unit could be getting an early start. (via OLV)