I received this Jack Nicklaus signed photo TTM in the 1970s. It came with a TLS where he answered a question of mine. The TLS is signed in blue ink with a regular pen, not the same pen as the photo.
My guess--and it's just a guess--is that the signature very much resembles a 1961 newspaper sports cartoon that he signed for me in the mid-1990s (see attached). When I sent him another sports cartoon to sign about a year later, he wrote that he wouldn't do it as he had a record of already signing something for him (the '61 cartoon).