more #

with astonishing speed, my friend Chris replies: "the '#' symbol is the 'hash sign', which is i think a popular
corruption of the original 'hatch sign' (good old Oxford English
Dictionary). the sense of hatch is to mark or score (think
tally) hence the use as indicating number."
of course!
and even a fairly cursory Google search reveals that this subject has been fairly extensively explored many times and in many ways by many people - there's an entertaining if slightly splenetic commentary here for example, and a very learned newsgroup exchange on the 'octothorpe' aspect (see how quickly we adopt the lingo) here.
the relationship with number is clear - probably goes back a very long way.
less clear is its function as a game (our noughts and crosses is obviously a relic of something much older) - which has nothing to do with counting, or as a musical notation: how did this , for example, come to mean that when you come across the note 'C' in the piece of music here notated, you must play it a semitone higher?
further, what relationship, if any, do these usages of this fairly universally occurring symbol have with the Chinese pictogram for 'well', as used in this diagram of the constellation Ishuku?


hmmm
*scatches head*