Baseball cards are very popular for cut signatures.
This means that whatever the player signed in his history (such as cheques, letters, bank slips etc.....) they cut up and stick them on a card just like a GU card.
The players on this card are legends of baseball and continually bring massive prices for their autos.
You could compare them to the MJ's, Birds of your game. I am not really a basketball fan.
The difference is that these players were around at the beginning of baseball and dominated the game.
The best equivalent I could give would be like Ron Barassi, Teddy Whitten, Jock McHale and other heroes of AFL.
I am watching this card so I will post when it has finished just to show what something like that would cost.