80 and X

We've see countless cars bearing a sticker on the back windshield that says 80.

I've seen it so much I've stopped seeing it. Nadir has revealed its meaning.

That is the mark of a student driver. When they achieve their license they must not exceed the speed limit of 80 (kilometers not miles) an hour for two years.

Nadir, however, could not explain all the X's hanging from the rear-view mirrors of cars in town. The rectangular X signs are sachets, yes, I know, but what does it mean?

X marks the spot? Malcolm X? Is there a men's cologne with that mysterious name? Don't know.