How does Betsy let Tim know that Sam is back in town?

In Chapter Three, Betsy motions Tim outside and asks him if he would keep it a secret if Sam came back. Tim misses his brother, but he tells Betsy that he wishes Sam would return the gun. Betsy dismisses him, saying that Sam needs the gun. She makes Tim to swear to keep Sam's return a secret. Because Tim wants to see his brother, he promises to keep it a secret. For weeks, Tim watches Betsy, waiting for a signal that Sam is back, but when he tries to ask her she hushes him. Then one day, Betsy comes in to buy beer, and she gives Tim a small nod, a signal that Sam has returned.