Actually this option is available on most forums that don't allow Sock Puppets. If you are really suspicious that someone is a sock, you can usually ask the administrator who will check it out. That is a better way than making unsubstantiated, false accusations.
And whether you know it or not that is exactly what occurred at a forum you used to participate on, with one of YOUR socks.

And it wasn't even me that asked, but someone asked the administrator, who looked into it and discovered it was a sock of you.
I really don't care all that much about socks, except in the case that someone making unlikely and mathematical impossible, or mathematically "very improbable" claims, creates a sock to provide credibility. That is very often the purpose of these socks.