Notice the act of motion (delineation of the ring)?
He extends his right hand with episcopal ring...
The ring meets you. It is a sign of his jurisdiction. He is wed to his See. You reverence it in homage with a symbolic kiss.
The Rome tour guide always says a bit about papal portraiture at the very end of the Pinacoteca gallery in the Musei Vaticani as there is an act, practice, or art of making portraits.
It is subtle, but subliminal and is symbolic of the obeisance due in token of so much.