protective symbols for stones

so I have a small black obsidian mirror ( kinda ) its smallish , about the sise of my palm and used as a necklace or endant simuilar to this but flatter and bigger and completly ´polished

http://1.bp.blogspot.com/_sf9gHRBJV...lar+macrame+plata+gris+hunab+ku+obsidiana.jpg


wich I use for scrying and as far as I've heard , at least with crystal balls , you should use a protective rune synmbol etc. and I think I need it s:

obsidian is protective of course , but it also brings harsh thruths and it is said to show everything and might be a little too powerful for me at this stage n_n;

but I dont know of any s: so could you give me a hand? or perhaps just write a prayer or something on the back of it? or perhaps just the intention of it? or something?

Im was raised catholic , and there are some kickass catholic prayers XD lol although Im agnostic now , perhaps panteist , but not in the nature loving and worshiping kind of way X) but as in the universe

but then again it isnt too big for me to write a whole prayr lol, so do you know of any symbols? or how do find them , or what do you use as pretction?

I was perhaps thinking of something related to Tezcatlipoca perhaps? after all he is the god of divination , obsidian , scrying and pretty much everything related to obsidian mirrors XD lol

I usually use Runes when I need protective symbols. I meditate on the one that I will use since many of them can be used for protection.

You could also invoke a Tarot card to protect and use the symbol/number of that card for protection. You could choose the card yourself and pick a card which feels protective or has a black obsidian-like feel to it. Or you can ask your deck which card would promise to protect it.