[Brian]

We're not sure how it got set - the other person that had this problem was actually british, so it was even weirder that it was set.

The default state of the system as we understand it is to not have that setting there at all; that means 'just use the system preferences setting'. So the commands I suggested are basically just restoring the intended status quo.

However, if some application set that, or is dependent on having that setting set a particular way, it'll now probably be a bit confused. Since we didn't write the app, or know what got the setting that way, we can't predict much more than that.

One thing you could try would be to run these two commands, which restore those defaults settings, but with a slightly different behavior. (The '#' character, in this context, means 'any digit can optionally go here'.)

defaults write NSGlobalDomain NSPositiveCurrencyFormatString '$####.##'
and
defaults write NSGlobalDomain NSNegativeCurrencyFormatString '$####.##'

A specific number means 'if I don't type a number in this spot, add it for me', which is why you were getting what you saw before.