Found a Strange Sign in an abandoned Fort?

Me and a couple friends walked into a restricted fort from the 19thcentury. It was built into the ground and we needed a lighter to light our way in the dark paths of the underground bunker. We saw old antiques and some dead animal skeletons who couldn't find a way to escape out of the darkness. Then we came across a weird sign that looked like a dagger pointing downwards and 3 snakes curling up its blade. It then said underneath the sign "Hear us! we kill, we fight, we live! Forever and ever death to the smallest lamb!" We all got really scared and left after that. What could this sign mean?