It seems like some type of filming or pre-production stage is taking place for Transformers 4 today in California. Here is an article from Comic Book Movie discussing the possibility.
It was previously stated that director Michael Bay's fourth Transformers film would begin shooting sometime in May, but a new report suggests that production may actually begin today. On Location Vacations received a tip saying that "something" for the movie (which is described as the first of a new Transformers trilogy by Bay) is being done today at Raleigh Studios in Playa Vista, CA. However, it's unknown if this is merely pre-production (such as visual effects or screen testing) or if filming is actually beginning. It is also unknown where the majority of on location filming will occur, but it has been confirmed that it would be different from the prior Transformers trilogy, as the fourquel will be completely redesigned.
If they are indeed filming, this could be for a scene much like the moon landing in Dark of the Moon, which involved none of the movie's stars.