I told my #1 they were #1 and they said "thanks for telling us." Nothing else. No further communication. I ended up matching there.
My advisor told me that programs often do NOT like to hear that "they are ranked in the top ___on your match list." He said it makes you sound arrogant and does not make them want to move you up on their match list...in contrast, some programs DEFINITELY DO move you up on the rank list if you tell them you will rank them #1 (ie. not #2, not #3, not "top 3"). I know this latter fact 1st hand: my TY program director told me that telling him that we were ranking them #1 helped me and my S.O. couples match there.