I'd seek out advice from folks who have actually accomplished this successfully on similar bats with similar finishes.

My 2 cents: As was suggested, do NOT use sandpaper. And the problem with using a solvent to try to disolve the signature so that you can wipe it off is that this only would work, in my opinion, if there is enough of a sealant of some sort covering the surface of the bat such that the ink did not sink into the grain of the wood. If the ink has been absorbed into the wood, as opposed to just sitting on the surface, I think removal of ink without removing at least some wood by using an abbrasive (such as sandpaper) would be pretty much impossible. And it seems to me that glossier and more substantial finishes were not used until after '76. But this is all speculation on my part. Check with folks like John Taube, etc.