I know a few people have had a problem with this and so did I so here's what you need to do to add a siggy

go to your profile
preferences - scroll down and click yes on always show sig on post and also click yes for html - SAVE
go to signature - add what siggy you want (your name and html for any blogs shops etc you have) - SAVE
and hey presto it now works
If you still have a problem pm me as I am able to do something on the admin side