I have a 1954 team signed New York Yankees baseball with 5 Hall of Famers on it. When I was little and showed it to my friends, the signatures started to smudge a little so my Mother put clear nail polish on it to protect it. Is there a chemical I can use to eliminate the polish without hurting the signatures?
It would depend mainly on the chemical composition of the ink (permanent marker? standard ballpoint?)
If it was signed with standard ballpoint, you have a problem, because the main film forming / thickening agent used for ballpoint pen ink is the same used in the majority of nail polishes - nitrocellulose. This means that a solvent that removes nail polish (ethyl acetate, for example) will also remove the ink.
Nail polishes use solvents such as butyl acetate. If the solvent dissolves the ink, it would have destroyed the signatures when the polish was applied. Therefore you should try to use a similar solvent (e.g., ethyl acetate) to get rid of the polish. Use a cotton swab soaked in the solvent and try it first on the least valuable signature. If it works you can apply it to the rest of the baseball, but be warned that the signatures may appear more faded afterwards.