The perpetually cash-strapped MTA is apparently going to be swelling its coffers by allowing advertisers to target straphangers who use the Union Street subway station. Over the past couple days we’ve seen workers putting up frames at the formerly ad-free station. Though we’ve been fans of Union Street’s sparse look, we’re going to take solace in the fact that the Gowanus/Park Slope R stop is not likely to be sponsored by Mickey & Co. any time soon. Anyone noticed ads being introduced to other Brooklyn stations? GMAP