Rep Points for Signatures with Links

is there any way to add a condition that only allows users with a certain amount of rep points to have links in their signatures?

This is not built in to vbulletin. it will have to be custom coded.

Switch off signatures for your regular members, setup a secondary usergroup called 'Can have signatures' (or something like that) and allow that usergroup to have signatures (as it is a secondary make sure everything else is swiched off).

Then goto usergroup promotions and setup a promotion based on rep points.

Good idea. I didn't even think of that.