In baseball memorabilia, you wouldn’t collect a bat signed by a pitcher or a glove signed by a designated hitter. Well, some people probably would, but it’s more likely you’d want a baseball that had been autographed by a pitcher like Sandy Koufax or Nolan Ryan, or a bat that’s been signed by sluggers such as Hank Aaron or Willie Mays.

Similarly, the most collectible footballs are signed by the players who touched them the most. That’s why football memorabilia collectors usually look for footballs autographed by quarterbacks such as Joe Namath, John Elway, Joe Montana, and Johnny Unitas, or running backs from Jim Brown to Walter Payton. Receiver signatures are popular, too (Jerry Rice and Mike Wallace are favorites), but how do you account for the popularity of Troy Polamalu’s autograph on footballs? Maybe it’s because footballs rarely get past this exceptionally strong, strong safety.

In general, footballs signed by players of the last quarter century or so are commodities—forgeries and reproductions abound, so make sure yours comes with authentication you can trust. More rare are footballs whose signatures and pebbly pigskin surfaces are both vintage. Nineteenth-century footballs were melon-shaped, harkening to the sport’s lineage in this country from rugby. Spalding claims it manufactured the first American football in 1887, but even these were not as pointed at the ends as footballs are today.