Simpson said Friday it felt "strange" to be signing autographs in such a venue. He said it did not occur to him that the date nearly coincided with the 10th anniversary of his Oct. 3, 1995, acquittal on charges of murdering his ex-wife Nicole Brown Simpson and her friend Ronald Goldman.
"I don't keep these dates in my head," he told The Associated Press while signing various items with the inscription "O.J. Simpson '68 Heisman," a reference to the year he won college football's Heisman Trophy.
He said the only anniversary he observes is when he and his children mark their mother's birthday with a cake.
After playing at the University of Southern California, Simpson became one of the best running backs in NFL history, mostly with the Buffalo Bills. After that, he was an actor, television football commentator and pitchman for Hertz.
Simpson's appearance Friday night was a private affair in which he was presented with items sent in by collectors who paid in advance for his signature.
Fans who prepaid $95 a ticket to enter the convention later in the weekend will have the opportunity to buy memorabilia and also get Simpson's signature, as well as buy souvenirs of horror films and comic books.
"This is kind of an unusual venue," said Simpson, who now lives in a Miami suburb. "Friends were really excited when they heard I was coming to this, but I find this strange."