Latin proverb. Translates to "Nobody ridicules me unpunished". According to Edgar Allan Poe the motto of a rich aristocratic family in Venice during the Renaissance.
Poe describes how a young member of said family is jokingly insulted by his best friend during Carnival. Acting according to his ancient family motto, he lures his friend into the wine cellar, gets him drunk, and then locks the door from the outside and erects a wall in front of it.
The motto is also found on the side of a third of all British One Pound coins.