A coat of arms is a symbolic representation of the person's family lineage and heritage. It is a source of tremendous pride and respect for those who have a coat of arms. Usually, richer, more affluent classes boast a coat of arms. In the early days, a coat of arms was the insignia drawn on the sheilds of the knights as they marched into battle. Montressor says it is:
“A huge human foot d'or, in a field azure; the foot crushes a serpent rampant whose fangs are imbedded in the heel.”
“And the motto?”
“Nemo me impune lacessit.”
(No one insults me with impunity.)
Montressor's coat of arms is of a golden, impervious foot stamping on and crushing a serpent who is trying to sink its fangs into it. It is implying that yes, you may "sting me," but I will crush you.
The coat of arms that Montresor describes is so bizarre that it could be entirely imaginary. It is a huge golden human foot crushing a snake. It is also almost too appropriate for the occasion. The motto is also almost too appropriate. It may be that Montresor does not have a coat of arms or a motto at all. And it may be that Fortunato is being malicious when he says, "I forget your coat of arms." Fortunato may know perfectly well that Montresor does not descend from a noble line. Montresor is not committing this murder because of his ancestors or their motto. To suppose this is to negate the validity of the "thousand injuries" that Montresor mentions at the beginning of the tale. He may be describing a coat of arms and motto he would like to have. Poe gives many indications that Montresor is not Italian but French, meaning that he does not have deep roots in Italy like Fortunato. In the third paragraph of the story, where Montresor writes disparagingly of Italians, this is clear evidence that he is not Italian himself. This makes him seem like an outsider to older Italian families, and it is a social handicap as well as a handicap in his business dealings.