If there were deaf, why would they want the hymns to be signed? It won't help them sing...since you need to know the words ahead of time to sing...and churches that take singing seriously provide hymnals with the words - and post the hymn numbers before the ceremony.
Signing the sermons would make more sense....though printing the sermons ahead of time would make more sense.
We have signers for the deaf at one of the churches I belong to. One reason for signing hymns is to allow the deaf members to participate in that part of the worship together with the hearing members. Just as the hearing members like to sing as nicely as possible to God, the deaf members like to "sign" beautifully. It's more meaningful than just reading along. Also, many deaf people knew the songs earlier in life before losing their hearing, so the signing helps remind them of the worship songs.
I agree with the other poster that the priest with an agenda is bananas.