When it comes to stroller-stalking, the child-free readers of Gawker are pretty useless; they email all excited, "I saw Mike D. pushing a stroller!" but then they leave the real news--the KIND of stroller--out.
So I did some digging, and according to this image on a Beastie Boys website (for their recording studio, Oscilloscope.net), Mike D. rolls in an umbrella stroller.
The handle shape says Kolcraft, but the straight back, distinctive triangular shape, and black color say Maclaren.
But let's go to the tape: when he was Gawker-stalked, Mike D. "quickly crossed the street [in embarassment and shame.]" I'm afraid his own actions can only mean one thing: