Therefore, logic would dictate that posting a link should be a privilege granted by a specific Usergroup Permission.
This would allow Admins to only grant this permission to users who have demonstrated their commitment to the Forum (e.g. has posted at least X times, or received at least Y likes, trophies, etc.).
Currently, there is no way to keep new users from posting links unless all new posts from new users are moderated, which is overkill.
Any user wanting to post a link immediately is most likely a spammer, so this would easily fix that problem.