An initialism for "see you in the funny pages," an old-fashioned and jocular expression of farewell. (The "funny pages" refers to the section of a newspaper in which comic strips are collected.) I'd better be going now. SYITFP!
See you in the funny pages
and SYITFP
sent. & comp. abb. I will see you around. (see also See you in church.) Bye, Tom. SYITFP.