Quote Originally Posted by TosaInu
How about increasing the thickness of the string? I recall the Mongols (?) wrapped soft leather around the string where the thumb would grab it.

How about a leather thumb protector? A metal ring makes a smoother release, but a leather one is more comfortable. My guess is that a leather one would also be easier to recognise as a sort of tab too.
As long as the thickened area is at the nocking point only and could not be deemed as a means of aiming, at inspection. It would even be possible to fit those sleeves you sometimes see, especially on kids bows; but extra weight on the string only serves to slow it down. Most traditional Korean bows have thicker strings.
As you know, the traditional way to string the Asiatic bows is slightly different to western bows. A loop is tied, using a special knot, to each end of the string. There is evidence that these loops were sometimes wrapped in soft skins such as mice.

The thumbring issue I described is the current understanding within GNAS/FITA guidelines (though FITA does not recognise 'Traditional') It is possible that a leather ring would be permitted, it would depend on the judge and/or any objections from other archers.
There are other governing bodies that allow the thumbring but the rules applied to the bow become strict and a little contradictary

......Orda