Modular Dungeon V2

I don't understand Silk, what do you think this red symbol drawn on the floor means?

Tumlak, what a stupid question, it's a skull with bones, drawn with blood... it's obvious that beyond this door there must be something of the highest value, something that we absolutely must make our own.
So let's go now, my dwarf friend, open this door... but I'm waiting in the other room