Most modern stickers use a solvent based adhesive which is weatherproof and has been designed not to adversely affect painted and or plastic surfaces.
There are always exceptions to this and as the substrate preparation etc is beyond our control we cannot be held responsible for any damage that may be caused by application or removal of stickers.
Having said that, we have produced millions of stickers that have been applied to thousands of vehicles around the world and have yet to experience any sort of serious problem.
It is during removal that you are most likely to damage your paintwork but a couple of simple tips should eliminate any problems:
1) Use a heat gun (or park the vehicle in the sun* *not applicable in the UK ) this will soften up the glue.
2) Do not use any sharp implement - not even your finger nail, its not necessary. Just get the sticker warm and rub the edge with your thumb and it will start to come off.
3) Then peel the sticker by rolling it back across itself (like folding bed sheets back) - not pulling it upwards like opening a car bonnet - this will put the least tension
into the paintwork. If your paint work is well applied and keyed to a good surface the sticker will pull away cleanly.
4) Depending on how long the sticker has been applied and the conditions of removal there may be some glue left behind. Use a soft cloth or paper towel and some brake cleaner, Wd40, Washing up Liquid etc to remove the glue, do not use Petrol.
5) If necessary polish the area the sticker has been removed from.
6) Don't forget the most important bit, buy some more stickers to replace the old ones!