what does "Yee-Yee" mean? i see it on the back of vehicles on stickers on windows.

Its basically like "Yee Haw" but for pavement princesses

I have no idea and I’ve never heard of such a thing, but this is from urban dictionary:

An exclamation used by hunters, fishers and other country folk when just about anything happens. It's used under any circumstances usually with the phrase "live action" added in before. Hunters will occasionally raise their guns in the air to exclaim a yee yee. (Yee may be repeated more than twice if appropriate.)

It used to be slang for cocaine when I was in high school but slang changes over time and with location, so I don't know if that's still the case for this particular instance.

I would say that it's a bumper sticker, an exclamation, to show that the person driving is fun-loving and country-loving.

Has similar vibes to YOLO (you only live once) as well.

Aw, yeah
yeah yeah yeah yeah
yea yeah
yea yea, yea yea
yee yea
yee yee yee yea!
yee yee!