Hello Bjorn, We do not recommend using anykind of stickers except the official set that we provide for Alveo or Vertex Helmets. Regarding the inspection of your helmets we recommend that you remove the stickers to clearly view the shell, to remove the glue use a gentle cloth to clean the surface with methylated spirit, do not dip the helmet in the methylated spirit. In the future avoid the personalisation of the helmets except if done with the specific petzl sticker kit and specific application areas. Thank you for your interest. Sincerely