FWIW, I think that signatures should not be allowed to have links at all...and if they do have links, they should definitely not be allowed to have commercial posts.
I think the policy changed a while back to allow links/commercial type posts for 1 major reason (and this my assumption, not facts):
Mods were not actively enforcing the previous TOS because it was a pain in the neck to do so, so rather than actually enforce the "law", the "law" changed to suit the norm.