No there's no way for you to check yourself whether the software was registered. However "registration" itself doesn't mean much. It just means if for some reason Microsoft decided they wanted to see who owns a particular CD key, they'd look and see it's Mr. Smith. But if Mr. Smith sold it to you and gave you the certificate of authenticity (now just the little sticker on the side of a computer) then you own it, and if Mr. Smith still has copies of it in use then he's the one who is breaking the law. Naturally, if you register the OS when you install it, Microsoft is going to see that it's been registered by two different people, which is why the only way to absolutely avoid an issue is for Mr. Smith to call Microsoft and notify them of a change of ownership. But if you don't register it during install, then there's not likely to ever be any problem.
"Activation" is a separate issue from registration, if that is what you're actually wondering about.