Oskar is in the art store and finds the name "Thomas Schell" written throughout the store.
"His name was everywhere. He'd tested out markers and oilsticks and colored pencils and chalk and pens and pastels and watercolors. He'd even stratched his name into a piece of moldable plastic, and I found a sculpting knife with yellow on its end, so I knew that was what he did it with." (Pg. 50)
The significance of Thomas Schell being written all over the place at this art store is questionable, at least this point. Perhaps it is meant to create confusion within the reader, and perhaps doing the same to Oskar, while at the same time inspiring him to continue trying to find whatever-it-is that his father encouraged him to find on his last scavenger hunt.
Oskar's grandfather lost his ability to speak, and is forced into a world of sinlence. His only remaining way to communicatew ith people is by writing words in blank books.
On page 233 Oskar's grandmother is talking about his grandfather leaving her " When your grandfather left me forty years ago, I erased all of his writing. I washed the words from the mirrors and the floors." This shows his grandmother cleansing herself of the grandfathers memory.