UNO do I need to call it again?
The official rules state:


  When you play your next-to-last card, you must yell “UNO” (meaning “one”) to indicate that you have only one card left. If you don’t yell “UNO” and you are caught before the next player begins their turn, you must draw two cards.


It says nothing about calling UNO when your turn comes up or if you somehow end up with 1 card in your hand via other means (swapping hands, etc.).