I thought for a few minutes about the reason that units of currency are different and come before the number, determined there must be an obvious logical one. But, if there is, I can't think of it!
I suppose it's also possible it needs to sometimes be used (although, again, I have never seen this) in certain cases in more 'formal' situations - accounting, contracts and so on. I guess the format, with the symbols wrapping the numbers so as to make them easier to parse, does make sense.
Similar rationale, though, because it's easier to modify a number (say, change a 7 to a 9) than to change a full word.
#$105.90#
Is this just local to me?
From the same source, "an R-value expressed in I-P (inch-pound) units[13] is about 5.68 times larger than when expressed in SI units"; the latter being measured in K⋅m2/W.