Depends on where you live mostly.
Here in AZ, you can visit the local police dept, with the frame. They will tell you if the frame # has been reported stolen on THEIR database.
Note that you cannot get it registered. In order to get it registered, it has to be a roller, with an engine, and "look" complete. It then has to be trucked (unless you were ignorant enough to restore before confirming title) to the Office of Motor Vehicles (OMV), where they will run it through a DIFFERENT database. If it has not been stolen, you can then fill out some more papers, they will send a letter to the last registered owners address, and if no response, you can get a bonded title after a couple months and around $150.
HOWEVER, if the OMV database shows it stolen, they will confiscate your bike. Right there, right now. This happened to a forum member on another site I am on. Note that after a few more months of OMV investigation, he was able to get the bike back. But if the person whom it was stolen from 20 years ago happened to be found, and said "YEA, I want my bike back!" he would have been f'ckd. Xcuse my French.
If you happen to be in NH, its a bit different. While still here in AZ, I bought an un-titled Yamaha DT175 to strap to the bumper of a Motorhome. (Keep the ad where you found it for sale, and get the sellers name, address, and DL #...) Got it running without too much effort, and trailered it down to the local PRIVATE ( a lot of these are popping up in my area) OMV, and the dumbass manager looked at the VIN, and declared I must had stolen it and altered the #. WTF? She would not even run it through their database, as it was not a full 17 digits and she did not want to get involved with "... an obvious illegality". I actually had some printed info from this site regarding frame serial numbers with me, and she would not even look at it. I am not making up these words. I find it staggering how stupid some people can be. She must really think that someone would risk jail time over a $500, 40 year beat to sh!t motorcycle. ???
So I put the DT on the bumper, and we proceeded to take our vacation to a small town in NH. Where I went to their OMV equivalent. They told me a LEO had to inspect it, and he could come by the house a few hours later. He did, I filled out some forms, they ran it through their database, and my brother-in-law sent me the registration a few weeks later.
Yes, registration, not title. As NH does not issue title for motorcycles over 20 years old, per their OMV website. Weird. My next step is to take the NH registration to my downtown, REAL OMV (hopefully they will be a little brighter) and try to get a REAL title.
A bit of a pita, but watcha gonna do? I'll update this thread with my results in a couple weeks.