So unfortunately we can't set ship mottos in game, it would be really cool if we could though. That hasn't stopped me of course.
My daily driver, the USS Thunder Child (Mirror Strike Wing), has the wonderful motto of: Qui Tangit Frangitur (Who touches me is broken)
Or translated to modern parlance, FAFO. Shameless stolen from the HMS Repulse.
What are the mottos from your ships?