This mantra shows up everywhere in the Ferris Bueller movie universe. On the town's water tower. On the marquee at Wrigley Field. On a kid's binder at the end of the film, where it's given some hardcore side eye by a defeated Ed Rooney. It demonstrates just how much Ferris means to the Shermer community.
The "Save Ferris" movement also suggests Ferris's legendary, nearly god-like status in Shermer. When word gets out that he's sick—and just how does word get out that he's sick?—the news spreads like wildfire and grows to epic proportions.
When Ferris's parents last see him in the morning, he has clammy hands and feels weak. Meanwhile, at school, Jeanie encounters one student who's started a collection to buy Ferris a new kidney, and another who says that if Ferris dies, he's donating his eyes to Stevie Wonder. When did death enter the equation?
The "Save Ferris" motif is used not only to show Ferris's power and the reach of his charm, but also to gently poke fun at the citizens of Shermer and their suburban naiveté. Oh, and how's this for irony: Why does Ferris take the day off in the first place, Shmooper? That's right: to Save Cameron.