I can't really say much about the Fraser motto, but having lived in France (or a French speaking community) for 28 years, and considering myself a fluent French speaker, the phrase "Je suis pres" (without the final "t") means "I am ready". If you add the final "t", it doesn't mean anything. "Prest" is not a French word.

Maybe a mistake was made long ago and they've just kept the motto with the mistake? I really can't say.

Hope this helps.