Denatured alcohol is used as fuel for various dental and jewelry torches.
It is not particularly dangerous. It is sold at hardware stores and paint stores (in California!). I bought mine at Lowe's.
To answer your question, the imprint left by the decal looks worst than it really is. It is hardly noticeable after the alcohol dries. When back in the car, no one would notice it unless you pointed it out to them.