How is one able to tell if they have a genuine Rubik's domino..old version..from politoys..? I acquired an old set of cubes and this was in there...from pictures, I think it is genuine but are there any distinguishing marks that will verify this?

If the turning feels particularly tight then there is a good chance that you have the old Groove Mechanism domino by Politoys/ Politechnika.

Other than that just looks for signs of wear on the plastic; either for scratches on the cubies or dust on the inside where the plastic has been ground down.

Hope this helps.

For all Domino questions Thomas has a wonderful thread here.

Note by "original" I believe you mean the spindle mechanism, and you can distinguish it by the "321" configuration rather than the more common (and not as solid) groove mechanism which is "123".

Dave