In Bud, not Buddy, Bud's mother had what pinned up to her wall?
We are told this piece of information before Bud actually realises that the room that Miss Thomas has put him in is his mother's room. He suspects that the room is the room of a girl who has now died, which makes him nervous, but he does take time to notice what has been stuck on the wall:
The best thing in the whole room was one wall that was covered with pictures of some horses cut out of a bunch of magazines and stuck on the wall with thumbtacks. It looked like someone went through a lot of trouble to do it, each picture was held up with four thumbtacks and there were so many of them that they were like wallpaper from the floor to the ceiling.
Of course this says a lot about the character of his mother and her careful, dedicated ways. It is interesting that Bud's attention is drawn to this "wallpaper" display of horses on the walls, and this is soethign he refers to again later on in the narrative. The irony of Bud being placed in his mother's room is something we later discover.