'Raido' is the rune that looks like an angular capital "R", with one leg folded in half. All my sources peg it as a protective rune, specifically for travel and travel-related causes.
Something else you could use, if you use air fresheners at all--find one in the shape of a footprint, and draw wings on it. Hang it from your rearview, and voila! De-travel-funker AND protective agent! (With all the traveling Hermes/Mercury did, it's little surprise some consider him to be protective of travelers) Amber is good, as is moonstone; keep it in the center console, if you have one. (Haven't ridden in a Crown Vic, sorry.)