How do you get signed baseball cards authenticated?

Question

My dad has a great signed baseball card and signed baseball collection. He wants me to find a buyer, my problem is, they all want certificates of authenticity. My dad would attend baseball card shows in the 70's where the player would make an apperance and my dad would have these things signed. So how you get these things authenticated?

Answer 1

http://authentic.com

http://ebay.com

http://wal-mart.com

http://target.com  

Answer 2

beckett.com

psacard.com

Answer 3

there are companies that do that, just go to google and search that and a company should show up like PSA grading or Beckett