The proliferation of cards saturated the market, and by the late 1990s, card companies began to produce scarcer versions of cards to keep many collectors interested. The latest trends in the hobby have been "game used memorabilia" cards, which usually feature a piece of a player's jersey worn in a real professional game; other memorabilia cards include pieces of bats, balls, hats, helmets, and floors. Authenticated autographs are also popular, as are "serially numbered" cards, which are produced in much smaller amounts than regular "base set cards".