Since January 1, 2014, all softball bats must display the stamp to the USSSA 1.20 BPF stamp (shown to the right) for it to be legal to use.
This standard was put into place due to a number of altered bats finding their way into the youth fastpitch program. When a bat displays this stamp it means that the bat has been manufactured in such a way that if it ever becomes altered in order to increase performance beyond the 1.20 BPF limit then it will show very dramatic visible damage (e.g. cracking) to prove that it's been tampered with. In short, a bat with this stamp is either unalterable or, if altered, it becomes unusable.
The linked document titled “Illegal Bat Penalty” describes the penalty for using an illegal bat. We encourage all USSSA directors, umpires, coaches, parents and players to take the necessary steps to avoid the use of an illegal bat prior to and during a game.