It's very simple what you found.
It's a pentagram surrounded by the Zodiac...
The Zodiac is the stars and how our earth moves through it.. it goes in order.. The pentagram has been a holy symbol of power for eons.
The pentagram is also used in pagan, wiccan, gnostic, and many other groups in ceremony and ritual.. The upright one for invoking and the one hijacked by satanists for banishing..
http://www.themysticcorner.com/image...ac_Pendant.jpg
http://www.celtic-fringe.com/acatalog/BM127.jpg
I highly doubt what you found had anything to do with a Satanist or the Devil, more likely a pagan lived in your house before and some wind or something moved it, or the tape someone used stopped being useful.
Maybe you were meant to find it to do research and open your eyes?