There was also discussion there of the history of numerals. An earlier post on this blog dealt with ancient counting (aloud, names of numbers: Score! and counting sheep in prehistoric languages) but now the question is about writing numbers down.
A link was brought to this explanation. Some of us were skeptical, and someone's looking into it:
Fun With Numbers (and an illustration from that page):
Pam Sorooshian found this: http://nostalgia.wikipedia.org/wiki/Arabic_numerals/Talk
Google will turn up tons of cool stories. Here are portals to a few:
If you have any theories or favorite stories on numerals, or sites about their history, or personal stories, please deposit those below!