Background: Shawn Spencer (Psych) states in
Poker? I Barely Know Her that he doesn't wear jewelery, yet he is seen in many episodes wearing a chain around his neck.
Case: Is the chain part of Shawn's character or does it belong to James Roday?
Evidence:
Here is an image of Shawn from
Poker? I Barely Know Her:

There it it, the chain PrincessShawn was talking about.
We also see the chain in several of the
Psych photo shoots, such as this one:

PrincessShawn wondered if the chain might be James', so lets see...
Here is an image of James Roday at USA Upfront 2007:

I believe this image gives us our answer. If you look closely to the left of his neck (our left, his right) you can see just a little of a chain. The chain appears to be identical to the one we see in
Psych and the photo shoots.
Conclusion: These findings lead me to believe that the chain is indeed James', as he is seen wearing it consistently, on and off the set of
Psych, however I will not even begin to speculate what is on the chain, that is, assuming there is something on the chain.
Final Notes:
I do not mean to present any of the above as fact, as it is purely speculation and deduction.
I hope this isn't too creepy for James, if it is, just say so.
I apologize for the corny format I wrote this post in, even
I had trouble keeping a straight face while writing this.
Well, this was fun, but it's about time I went off to work.
6 hrs 37 mins until
Psych