"4s Up" is the UCLA Bruins recruiting symbol. Sources suggest that 4s refers to fingers. The "s" makes it plural. 4 fingers up on each hand = 8 (8 clap).
Of interest, when you hear the name 'Bruins', one school comes immediately to mind: UCLA.
Given that UCLA is the Los Angeles branch of the University of California system, and the bear is on the California state flag, it made sense for UCLA to adopt an ursine mascot. Initially, UCLA teams were known as the “Cubs,” while the University of California at Berkley went by the “Bears,” and later the “Golden Bears.” But students at UCLA resented the little brother status and rejected the Cubs nickname in favor of the fiercer “Grizzlies” nickname.
The Grizzlies moniker lasted just two years. In 1926, UCLA joined the old Pacific Coast Conference, which already had some Grizzlies in the mix -- namely, the University of Montana. UCLA agreed to give up the Grizzlies nickname, and Cal bequeathed UCLA one of the variations on their Bear nickname: “Bruins.”
Find out more on how UCLA acquired bruins team nickname at SI.com.
Check out The 10 Coolest Handshakes In Movies And TV compiled by Complex.