Setting for signatures affects the `url` BBC in entire posts

[isaak654]

Description

This was reported on the Bug Reports board (relevant details are on page 4):
https://www.simplemachines.org/community/index.php?topic=580848.60

If you disable url BBC, all links in topics stop working and not just in the signature:

So signatures should be separate from posts when it comes to the url BBC.

[DiegoAndresCortes]

@BrickOzp Do you think #7068 is related to this issue?