Gary Crawford, a Chicago resident who runs the website negroleaguelegends.org, reported the theft to Birmingham police.
More than 25 former Negro League players signed the replicas, Crawford said. One replica bore the image of league founder Rube Foster while the other showed an unnamed player sliding into home plate.
The replicas, taken during a banquet honoring former Negro League players, were to be displayed at either the downtown library or Alabama Sports Hall of Fame until a museum honoring the league is built in Birmingham, Crawford said.
"It's extremely historically significant to have all these signatures in one place. They're one of a kind," Crawford said.
"Perhaps someone took them by accident. Anything's possible. We just want them back. No questions will be asked," he said.