"Pa" St. Pierre

My great grandfather Charles St. Pierre (my mother's maternal grandfather) was evidently quite a character during his lifetime.  He was a French-Canadian carpenter, who helped build Chicago's Cook County Hospital.  The family used to travel back and forth between the family farm in Quebec and  the south side of Chicago.  "Pa" witnessed the Chicago Fire from the safety of the south side, and lived until he was almost 100.  He was still getting into fights at the local tavern when he was in his 90s, after which the police would drive him home. Pa also enjoyed teaching his children and grandchildren French swear words and expressions, which my sister Susan and I would hear from various members of my mother's family. Susan and I eventually figured out that one expression must have meant  "Eat Sh**."  My sister insists this was the motto on the St. Pierre Coat of Arms.  She is my older sister, so who am I to doubt her?  If it is true, it definitely explains a lot.