What was on sylvester hat in the movie over top?

You're likely thinking of the 1996 film "Space Jam", not "Over the Top". In "Space Jam", the animated character, Sylvester, is wearing a top hat with a "S" on it, for "Sylvester".

It's a classic cartoon trope, using a letter to signify a character's name, and it adds to the humor of the movie.