[cd34]

Sigs can however be blocked by group, and a user can be put into a group where 'Can Use Signatures' is set to no.

Short of someone being a member of Coppa, Unregistered or Awaiting Email confirmation, a user can always change their signature. If you got in before the Email Confirmation was confirmed, you might have seen that you couldn't change your signature. Once you validated, that restriction would be gone. I don't recall if that signature edit feature is blocked until the 10 minute scheduled jobs run or if it is immediate upon the validation.

I was under the impression though that the group removal was immediate after validation.