I picked up a copy of "The Racing Car Pocketbook" signed by DSJ. The seller actually said, someone has spoilt it by putting his name in it, not realising it was the author! I also got a paddock pass fairly cheaply at auction signed by Graham Hill and Jochen Rindt. Graham's signature I recognised, Rindt's took a bit of research. Genuine? I hope so I got a good price for it on Ebay.
Talking of Tom Baker, somewhere I've got a signed photo of one of his companions, my late girlfriend was a friend of Louise Jameson (Leela) and got her to sign several for my then young nephews. She, Antonia that is, had several odd scraps of paper signed by famous people whom she happened to see when working as an Amex rep in various swanky West End restaurants. Seems to me that autographs on odd scraps of paper are more likely to be genuine than a signed book or photo.
Back when I had trade stands at Goodwood and other racing venues we were often visited by well known personalities. After a while I decided to get a "Visitors Book" much to the disgust of my helper who always described autograph hunters as stalkers. Strangely the numbers of famous visitors fell off after that...