Thanks for flagging this. We actually have a dedicated form for reporting any inappropriate adverts and it's at:
http://www.sheffieldforum.co.uk/misc.php?do=form&fid=19
The site in question appears (from their front page at least) to be a dating site and uses the word 'mature' to describe their target age group rather than alternative meaning of 'mature content'. If we have missed something, such as the banner itself containing offensive material, then please send as many details as possible via the link above.
