Users who have not visited in more than 5 years have had their signature and homepage fields cleared out today; the reasoning is that a large portion of the URLs being linked to in these where to sites that no longer exist, which in some cases where now adult related or resulted in ad pages at generic link farms.
Additionally, all offsite avatars have been cleared as well, as a large portion no longer existed. If you where using a remote avatar, which was cleared, please update your avatar.