Remove single users ability to post his sig

[c-pr0mpt]

Hi,
My request would be for the ability to turn off signatures for a single user. Without having to worry about the others on the forum. For instance, if a guy continues to post porn in his sig, I would like to just remove his ability all together to post one. But its not fair to turn sigs off affecting the others who did nothing wrong.

Thanks in advance.

[c-pr0mpt]

Is this something that is really hard to do? Should I just give up hopes on this hack?