A few different English dictionaries include "on the left" as a current definition for sinister.
From American Heritage Dictionary 4th Ed. (En-En)
> sinister
> sin·is·ter (sĭnʹĭ-stər)
> adj.
> 4. On the left side; left.
> From Merriam-Webster's Collegiate 11 (En-En)
> sinister
> a. : of, relating to, or situated to the left or on the left side of something; especially : being or relating to the side of a heraldic shield at the left of the person bearing it
> of, relating to, or situated to the left or on the left side of something; especially : being or relating to the side of a heraldic shield at the left of the person bearing it
The bar sinister? Calling that a sense of the English word would commit you to saying that "vert" is English for "green", "gules" is English for "red", "or" is English for "gold", etc.
From American Heritage Dictionary 4th Ed. (En-En)
> sinister
> sin·is·ter (sĭnʹĭ-stər)
> adj.
> 4. On the left side; left.
> From Merriam-Webster's Collegiate 11 (En-En)
> sinister
> a. : of, relating to, or situated to the left or on the left side of something; especially : being or relating to the side of a heraldic shield at the left of the person bearing it