Although Maniac lives in a dorm room at the YMCA, he spends most of his time hanging out with Grayson in the baseball equipment room, or the "band shell" as he calls it. If any place is home to Maniac at this stage in his life, this is it. Having a place to call home is very important to Maniac, as he's spent so much of his life moving around from place to place without ever being able to settle down for long.
It's not surprising that he becomes so attached to the band shell, even if it is just a humble baseball equipment room. As this is Maniac's new home, he wants to make it all nice and homely, so he paints the number 101 outside the door and calls the place "101 Band Shell Boulevard."
But before long, Maniac's on the move again. Sadly, old Grayson has died, so "101 Band Shell Boulevard" just isn't the same place anymore. Before he leaves, Maniac brushes over the number 101 that he'd originally painted outside the band shell.