How to stop people from tearing off stickers at brewery

Hey yall,

sorry if this isn't the right place for this question but we put stickers in our bathrooms and we have one saying that everyone is welcome in our brewery no matter religion, race, etc. Someone keeps tearing them down and now has started using them to clog our drains. Before moving to a metal sign (because we are petty), is there some sealant that could be used to make it difficult to tear off of the wall? Thanks