It's pretty amazing how reflective people get when they're writing on harpsichords or virginals. I guess there is a sense in having an insturment built that you really are making something for the centuries, so you get a shot at a statement that will jolly well outlast you. Many of them reflect on the brevity of life, the solace of music, or religion. Please send any you'd like to add.
Mottos that actually have appeared on harpsichords:
Mottos that as far as I know would be new: