they peel off because you are cleaning the glass with something other than water - at least in QLD thats how they work - we used to have big dramas keeping them on in our cars (my house ones, not work ones) cause we used galss cleaner and stuff.
peel it iff and clean the area with water and a clean rag, make sure the glass is dry and put the new one on. they stick easily, and only come off when you peel them, and leave no residue.
look on the piece of paper you get with your sticker, it should say 'use only water' to clean the glass, it works a treat, it took me about 2 mins total to put my label on before work the other morning.
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