About two months ago the signatures stopped updating entirely. The major problem was that the Armory, which we are always reminded is still in beta, was experiencing some problems. Last week the Guild Launch signatures stared updating again (thanks to the Armory working again), but with a twist. They now will update automatically every 6 days instead of every day. However, you can still manually recreate the signatures once every 24 hours if you just have to get your stats updated. (Although with that said, I have rarely seen the Armory update right after you equip new gear and log out... still in beta. Yup.)
Your old signatures will still work indefinitely, but they won't be updated anymore. To take advantage of the new updated signatures, head over to the announcement page and follow the instructions. Basically all you have to do is change one word in the html line for your signature; find the word "sig.php" and change it to "wsig.php". Poof! You're done.
What site do you use to make your graphical signature?