In "The Cask of Amontillado," what do the images and motto on the Montresor coat of arms suggest?

Poe's story, "The Cask of Amontillado" is full of foreshadowing and symbols.  The coat of arms of Montresor, the aggressor in the story, is no exception.

When he mentions the coat of arms, the description is that of a golden foot crushing a snake whose fangs are embedded in the foot's heel.  The motto, 'Nemo me impue lacessit' means "No one strikes me with impunity."

This motto and the images in the family's shield suggest that Fortunato is not going to be fortunate at all...rather, the opposite.  Obviously, from the speeches Montresor delivers, he feels as though Fortunato has struck him with impunity.  Fortunato, then, is the snake who has bitten Montresor's foot.  Montresor intends to crush the snake one and for all, and by the end of the story, the reader and Fortunato realize he has done just that.  By bricking him into a wall far away from where anyone will be able to hear his distress calls seals his fate (no pun intended) to become like the skeletons they encounter in the cellar. 

Gold--the color of the foot--has long suggested fortune, wealth, good luck.  Snakes have just as often symbolized an evil or forboding source...take the snake who beguiles Eve into eating the forbidden fruit, or the snakes in Harry Potter (symbol of the Slytherin House, the actual snake in one of the books), for that matter, as examples.