You know when you go to jiffy lube to get your oil changed and they give you that plastic decal they write the reminder date and miles on for your next oil change? You place it on the inside of the windshield yet it has no adhesive, just cling factor.

Find something thin like that can be cut to match your parking sticker; then affix the sticker to it. Place on the outside rear window when you park on campus and remove it when you leave. Test the plastic piece with a hose to simulate rain (no need if you live in So Cal) prior to placing the parking sticker on it.

Might just do the trick. If somebody steals it, just tell the campus police its been scraped and ask for a replacement.