What is the blue mustang use for in The Outsiders?

The Socs were traveling in a blue mustang when they pulled up and brutally attacked Johnny.

Finally, between sobs, Johnny managed to gasp out his story. He had been hunting our football to practice a few kicks when a blue Mustang had pulled up beside
the lot. There were four Socs in it. They had caught him and one of them had a lot of
rings on his hand--- that's what had cut Johnny up so badly. It wasn't just that they had beaten him half to death--- he could take that. They had scared him.