There are several instances throughout the series of people putting their index finger to their lip, usually in reference to the Milford School.
- Earl Milford's signature pose for the Milford School is a finger over his lips. When G.O.B. includes him in the Aztec Tomb illusion, Earl holds his finger to his lips. ("Public Relations")
- P-Hound puts his finger to his lip right after the vote, indicating they can't talk thanks to Michael's "no talking" rule. ("Flight of the Phoenix")