Is that a window stick like the ones you can take on and off? Or one that said not to put it on the back windows with defroster?

I just put 2 on my car about 2 weeks ago

It didn't have any instructions at all, so I can't say if you should use it with a defrosted window or now.

It's a decal that ain't meant to ever come off! (Seriously, I had to take the last two off with a straight razor.)