Originally posted by Zep Tepi:

If you hear the zip of arrows, clanging metal, or rattling bone sound, there are skeletons nearby. They are hostile to dwarves and animals. Skeletons guard towers or crypts. If there's no tower nearby, then there's a crypt. Sometimes crypts are buried in hillsides and hard to see. You will learn to thank the skellies for leading you to them.

I might add to this.

If thou shalt choose to craft the beloved and praised Stagbreaker, the mighty hammer of the Gods, thy may be pleased to realize that burial chambers become trivial.