a cloven hoof
a cloven hoofa symbol or indication of evil.
Traditional pictures of the Devil show him with the head and torso of a man but the legs and cloven hoofs of a goat. Therefore, a cloven hoof is a giveaway sign of the Devil.
1959 François Mauriac A Woman of Pharisees She had been a trial to him from the beginning, and now the cloven hoof was beginning to show.