A simple filter:
length(added_links) > 0
But if I try to add throttling, it stops working at all. I tried with the options:
Number of actions to allow: 2
Period of time: 3600 seconds
Group throttle by: user
Action: Block the user and/or IP from editing.
Then I tried adding links several times to a single one and different articles by the same (registered) user, but the user has not been blocked. Also tried different actions, like Tag the edit for further review, and Trigger these actions after giving the user a warning. Nothing works, the warning is not been shown too. And the hit count on the filter stays at 0.