It refers to mace spray that you can use for protection. It is similar to pepper spray. You definitely don’t wAnt to get it in your eyes !

Mace is often used by police or security guards, in some countries mace can be legal to own as a private person. It is a spray that hurts like H***!! Like pepparspray. If we talk about mace as a weapon it was used many centuries ago as a close combat weapon.

The sign is referring to mace spray.