Delux,
The description that accompanies the picture of this truck in the gallery states it has a three speed transmission. This means three forward speeds and one reverse, and as Grigg notes, the lever prevents the driver from inadvertently putting the tranny in reverse as he cruises into town for Goat feed and a six pack of Red Tail Ale.
The operator must lift the lock-out lever or the stick won't go into reverse.
Stuart