They are disabled globally for the forum so even if yours is turned on it wont show. This was done after Fubar's suggestion above when the board was first set up.
I've considered allowing them, but im worried that if everyone has them they will make the forum look a bit cluttered and could get a bit out of control. A lot of people dont like them.
Enabling it to allow just a single line of text might be an option though i guess.
Personally I wouldn't reintroduce them Nik. They make forums look like they are populated solely by teenagers, and really clutter up the layout - I much prefer getting straight to the information I want.
No sigs, they get so out of hand, there are normally only about 4 posts to a page due to massive sigs. The site is fab as it is. Shame you don't have a donation link. lol