Nothing too scientific I'm afraid just the sheer disparity between the the rise in the price of physical, and the fall in the shares. Combined with the falls in oil, it looks like a slam dunk. I've got some oil shares as a sort of crude hedge on my gold miners position, and I've just watched them tank. It's got to be good for the miners.
Edit to add; As a warning, all of my comments tonight should be taken with a pinch of salt. It's gone 1am, and i've been drinking since 5! I know that your savvy enough to make your own calls, but I'd hate for someone reading this to make any investment calls based on anything I said!