One of my two best friends is a Christian who is deeply entrenched within her church and faith. I, on the other hand, consider myself to be agnostic at best, and she knows this. We've had many discussions on the matter, and while she claims to respect my beliefs - or, rather, lack thereof - she bought me a necklace as a graduation present that had a cross pendant.
Knowing how I felt about Christianity, she decided to tell me that this particular cross was a Celtic symbol for "sister." As someone who has researched the Celts for quite some time now, I was immediately skeptical and decided to do what I do best - research to prove or disprove her statement. At this point I have been able to find no evidence to support her claim and am convinced that it is her underhanded attempt to start trying to convert me.
I know she will ask me why I am not wearing the necklace she gave to me, but while I do not want to lose her as a friend, I am not willing to compromise my personal beliefs to wear a symbol of a religion that I do not endorse or follow, nor do I want to lie to her, should I be able to help it.
How do I get past this without losing her as friend? Or am I already doomed?
The cross itself is not necessarily Christian. I can't think off hand what sources the cross has come from in religions other than Christianity, but what little I do recall is that it has multiple meanings, depending on which religion it may have come from. I'm not sure if that tidbit will help your feelings, but it could be a starting point for some research, if you like. I've always just viewed it as yet another pretty thing Christianity adopted somewhere along the way and don't worry much about it.
If I were in your place, I wouldn't offer the information on why I wasn't wearing it unless she asked. If she did ask, then you may as well be honest and say you don't really feel comfortable wearing it. If she presses on that, you can explain that its general use as a Christian symbol makes you feel uncomfortable, so you prefer not to wear it, but it isn't that you didn't appreciate the gift. Hopefully, she'll understand you don't mean her any ill will and she'll be okay with that.
My friend did something similar to this, actually. She got me a cross for my birthday once, and then some kind of Christian themed ornamental trinket later on. I was fortunate that she never asked why I didn't wear the necklace or why I never displayed the trinket, though...
Attach the chain to the bottom of the cross and wear it upside down. If she really was giving you the gift as a non religious symbol, this wont offend her. If she gave it to you as a religious symbol she will be offended, but not anymore than you should be.