In the english language the symbol # is used to denote a number, such as “order #12” or “customer #30”. In brazilian portuguese we use " nº " (abbreviation of the word “número”), as in “cliente nº 12” or “pedido nº 50”, or sometimes simply “pedido 50”.
It seems that the # symbol is hardcoded in the administration templates, so I would have to do a global find and replace to change this. I believe it would be an interesting and useful new feature if we could customize this from the admin options, just like we can customize the currency.
I would think the “best” solution would be to find instance of '#' and replace it with {$lang.number_symbol} and then add a definition of 'number_symbol' to your language variables. Then when using non English sites, you can have it different, but leave it '#' when the user selects an Anglo type of language…