To answer your question I pulled up the Tos of namepros and here is a snippet for you:
1.5) Signatures need to be set up in your profile. Signatures should contain no more than 4 lines. Please keep your signatures at a reasonable size. Do not place URLs or links to sites that contain explicit, vulgar, sexually-orientated, illegal, warez or obscene content in your signatures. Signatures may not contain any font larger than size 2.
So to answer I think you can have quite a few links just keep it to no more then 4 lines.
Hope that at least points you in the right direction