I think you have to delete the old siggy first and then enter the new one...I changed my siggy and it took a bit but then I realized that if I deleted the old one first and then added the new one it worked right across the board in all my posts

delete old
check your post to make sure it's gone
add new
check to see if it worked

I hope that helps

good luck

oh btw...when you change your profile you have to submit them each time