When Holden finds an obscene word on the wall of Phoebe's school, he (a) adds another; (b) corrects the spelling; rubs it off.

rubs it off

I hardly even had the guts to rub it off the wall with my hand, if you want to know the truth. I was afraid some teacher would catch me rubbing it off and would think I'd written it. But I rubbed it out anyway, finally. Then I went on up to the principal's office.