How do you authenticate signatures on two baseballs from the 1980s?

An autograph that is not authenticated by a creditable company could sell at half the market value or less. Two of the top, and most trusted authenticators are PSA/DNA, and James Spence Authentic -JSA Collectors will pay more for signatures authenticated by either one. It may sound odd but in some cases PSA/DNA, and JSA authenticated signatures may sell higher than a Letter of authenticity from an unknown or less trusted authenticator that witnessed the signing even though PSA/DNA, and JSA did not. It's just a matter of collectors trust, and collectors will pay more for it. Check the respective websites Show Schedule to see if they will be in the area that you live. They also do business through the mail. If you did not acquire the signatures yourself, or are not sure of its origin, do your homework. Before spending money on having the autograph authenticated find signatures on line that have been properly authenticated, and compare them to yours. If you feel comfortable that they are authentic then proceed.