dstiles - 10:50 pm on Jul 21, 2012 (gmt 0)
I only have "illicit" pound signs on this site - and not many other things on other sites. The entities seem to work fine (which is good).
I have always worked in ASCII (mostly 7-bit display characters, occasionally (in error) the A3 pound sign) although on a couple of sites we may have "smart" characters (quotes, dashes etc) which people submit from Word or similar. These always show incorrectly on our sites and as soon as found we change them to basic ASCII or entities.
Your test site uses entities of various types, not "invalid" symbols. For the pound sign it uses:
& pound ;
& #163 ;
& #xA3 ;
(spaces added to ensure display here)