The curse words scribbled on the school wall symbolize the loss of innocence that Holden fears and which is attached to adulthood. The curse words show that the children in the school are being shown something that is mature; by being shown these words, the children are being forced to grow up too early. THis is what Holden most fears (growing up) and it truly angers and upsets him that his little sister might also be exposed to this. What he loves most about her is her innocence; he does not want that innocence wiped away by anything. His brother Allie's death took his innocence, and his life and the life his family had was forever changed for the worse. Therefore, Holden sees growing up as something that one is forced to do, as the acceptance of a word that is darker and full of sadness and forced restrictions.
As lizbv mentioned the profanity on the wall. Another example would be the Little Shirley beans record.
The Shirley Beans Record represents a world without phoniness (innocence). Holden mentions the fact that he hates phonies several times in the book, and when he first talks about the record he mentions the fact that he enjoys the singer’s voice, and how she doesn’t sing in an overly cutesy way, as some children would. The breaking of the record symbolizes the loss of innocence, him fumbling to put it back together is a symbol of him trying to save the innocence that once was.
Holdens depiction on the catcher in the rye poem. He thinks it is " a body catch a body coming through the rye" though it is actually "body meet a body coming through the rye". This is ironic because holdens trying to save/protect innocence or catch it while "a body meets a body..." suggests a sexual act.