perhaps it has no source, and actually comes from somewhere else, like going up three times after you finish shmona esrei. actually, the reason for going up is because one is supposed to remain in their place until kedusha. at the beginning of kedusha one takes three steps forward, and then by kadosh kadosh kadosh one goes up.
i personally never did the pinkey thing, and as far as i know neither does my father. (although its been a LONG time since i davened standing next to him, seeing as i am female, so i could be wrong.)