Many currencies use symbols which are stylised versions of the initial letter of its name and for many of these the style used is indicative of the great age of those currencies, such as medieval script for old European currencies used since the Middle Ages.
It is not true that the Franc was 'just F'. It was originally an F with a line across the stem.
http://en.wikipedia.org/wiki/Franc
Deutsche Mark was 'DM' simply because it did not exist until 1948 so it would only ever be written in modern script. Previously the Reichsmark symbol was an Old German script 'RM', its precursor the Mark was a script 'M' and its pre-inflationary precursor the Pfennig was a script 'd' (denarius = penny= pfennig).
http://en.wikipedia.org/wiki/Pfennig
You can view numerous stylised currency symbols here...
http://en.wikipedia.org/wiki/Currency_sign