which finger points?

which finger of the yad יד points?

On a poster for the museum show The Precious Legacy; Judaic Treasures from the Czechoslovak State Collections you can see 15 "Yads."

Only one of these is left-handed (which does not surprise me). Of the remaining right-handed ones (made, primarily, of silver and wood with a little ivory and other materials) the hand is curled into a fist and the thumb points. Yet more odd, in another, the pointer is made of red coral (?) and the thumb (which serves as the pointer) is tucked under the index finger (as in the Signed English Alphabet "T").

Has anyone studied conventions for pointers? Does a database of them exist in any museum? If not, where would we begin to set one up?