I've seen this a few times in NY recently --
A pair of exterior mounted antennas, facing away from each other at about 45 degrees, I believe from memory BOTH are usually facing the rear -- it's not a radar antenna, I think.. since the cover is clear and has a bluish tint, like a laser gun's lense, however on closer examination, there is a small aperture inside about the size of a quarter.. The antennas are similar in size to your typical K-band or larger KA band ones.
Is this some kind of new hard-mounted laser, or moving laser? I looked for information from MPH, Kustom, Stalker, LTI, but didn't see anything new.