What do Slim and Whit discover in a pulp magazine? How is this important for the group of men?

Slim and Whit discover a "letter to the editor", written by a man who used to work on the ranch in the magazine.

Slim read, "'Yours for success, William Tenner.'" He glanced up at Whit again. "What you want me to read that for?"

Whit closed the magazine impressively. "Don't you remember Bill Tenner? Worked here about three months ago?"