[dmonitor]

The rationale I've always heard for having the $ at the beginning of the number was so that a handwritten value on, say, a check couldn't be modified by sticking a number at the beginning. 1.00$ could be forged into 91.00$, but not so with $1.00.

[tristor]

That rationale makes sense, and pretty much aligns with what I mean by a visual marker.