Colt Single Action Army revolvers, as well as double-action / hand ejector revolvers made between 1908 and about 1969 (with exceptions thereafter) have the double-step hand Red Cent and others have mentioned.
However while holding the trigger fully to the rear is supposed to result in a rock-solid, no wiggle lock-up in the hand ejector revolvers it doesn't do a thing in single actions - Colt's Ruger's or otherwise.
This is because in the double-action's the hand is attached to the trigger, so the further you pull the trigger the more the cylinder is rotated until it is locked by the bolt.
But in a single action the hand is attached to the hammer, so pulling the trigger has no affect on the hand.