I get alot of McFarlane Sports Figures base signed and to protect the base i take a plastic binder sheet and cut it open and wrap the base to protect the signature.

How would one go about protecting an autograph signed with a Sharpie over a plastic base? I thought about a clear lacquer or the like but am not sure if this would affect the Sharpie or the plastic, I don't know why it would, but I would like to get some input from the rest of you.

Thanks,
Mike