I don't know if it's actually a motto or if the Potter family had a motto at all, but on James and Lily's tombstone there is an inscription taken verbatim from the Bible: The last enemy that shall be destroyed is death. read more
Given that the Potter family comes from the Peverells, one may suppose that it’s not simply a typical insciption on a tomb, but rather a motto used to indicate the connection with the Deathly Hallows, the three magical objects that make one the master or conqueror of death. read more
"The Potter family is a very old one, but it was never (until the birth of Harry James Potter) at the very forefront of wizarding history, contenting itself with a solid and comfortable existence in the backwaters. read more
Hogwarts's (Hogwarts is Harry Potter's school) motto is"Draco Dormiens Nunquam Titillandus" which means"Never tickle a sleeping dragon". read more