Most of the fonts I own have the dollar symbol with only one vertical stroke, and sometime of those the stroke doesn't go all the way through the S shape instead simply projects from top of the S shape and from the bottom of the S shape.

But almost all old school typewriting machines have a double vertical stroke.

Most advertizements featuring price in dollars use a single vertical stroke. But, throughout the Hip Hop culture the double vertical stroke is most common.

http://www.google.ca/search?hl=en&q=hip+hop+dollar+sign+pendant&bav=on.2...

So what gives? Which one is 'proper'?

FYI, from Wiki...

The best documented explanation reveals that the sign evolved out of the Spanish and Spanish American scribal abbreviation "ps" for pesos. A study of late eighteenth- and early nineteenth-century manuscripts shows that the s gradually came to be written over the p developing a close equivalent to the "$" mark

There is a theory that the dollar sign goes back to the most important Roman coin, the sestertius, which had the letters 'HS' as its currency sign. When superimposed these letters form a dollar sign with two vertical strokes (the horizontal line of the 'H' merging into the 'S').

n.