Hi, SS
As usual, it's not that simple. I haven't researched the FFC clause of the US Constitution for a few years but, unless the entire area of the law has been overturned in the last few years, it doesn't really answer this question.
The bottom line is this: States are free to enforce their own public policies with their own laws regardless of the policies set by other states and regardless of the potentially contrary language in the FFC language in the US Constitution.
The FFCC is mostly used for RECORDS and evidentiary reasons. If you want to prove you own a piece of realty in another state, you can introduce that state's public records to prove it and the court in the state you're in can't question it just because it doesn't like the other state's record keeping.
It's one of the problems of living in a federation of states like the USA that it's hard to reconcile all the differences. That's why the same-sex marriage thing is a big deal.
If the FFC meant what you'd like it to say, then EVERY STATE would have to recognize a same sex marriage license issued in MA and every such couple would simply marry in MA and go back home and stick it to their home state.
But, as you probably know, it doesn't work that way.
If the question is "Did you register your MB in YOUR state?" Then, you could produce the documents from your state and they'd have to accept that you did, in fact, do so because the records SAY you did it. With nothing else to go on, the court will conclude you did register it.
But, that's not likely to be the question. The question is more likely to be, "Is this vehicle operating within the laws of OUR state." If not, you can get a citation. It just depends on what they're stopping you for. It's possible but unlikely you'll be stopped just to prove it's registered. Maybe the state you're in requires you to have a white light on at all times or maybe you can't exceed 15 mph or ride in bike paths, or you have to have fenders, etc., etc.
It's kind of the same thing as motoring from a rural area in the county into the Big City on your MB one day. In the county, maybe you were legal. But, as soon as you entered the Big City, certain city ordinances apply that don't apply in the county area. If you violate those ordinances, you're screwed.
So, if you choose to operate your MB in another state, you are expected, believe it or not, to know the applicable laws in that state and comply with them. If the only question is whether you reigstered it in your state, then they'll have to accept your state's records that you did as proof of that under FFC.
If that's all you're concerned about, then it's simple: just comply with your state's laws for registering. But, what if your state doesn't require registration for MB (as far as you can tell) and the state you're in at the moment does require it? That will be a tough one to sell to the cop. He'll be used to seeing documents and you don't have them. Anything could happen at that point.
I could be wrong, but I am not aware of any over riding federal law on the books at the moment that supercedes all state and local laws and protects you with respect to MB.
Here's another example: You can legally ride your motorcycle in some states without a helmet. If you ride into Oregon, however, we have a helmet law. If you didn't know that, you're screwed. You'd still be subject to stop and citation for riding without a helmet. They don't care where you came from and what the laws are in your neck of the woods and they aren't going to argue about it. As part of the stop, the cop will ask for your 'papers.' If you pull out some foreign paperwork that looks official, he'll be satisfied. But, he'll also ask for your proof of insurance. If your state didn't require insurance and thus you don't have it, TOO BAD. You've just violated Oregon law and you'll get a citation and you also get to figure out how you're getting home without your motorcycle.
Despite all this, if you actually had some documentation from your home state that showed your MB is registered (or whatever your state calls it), it would be impressive and it's likely that, if you weren't being an idiot, the cop would just let it go or tell you to stop using the motor. But, what if the cop's state requires insurance and you don't have it? Good luck!
I'd love to hear HoughMade's input on this.
Steve G.
Grants Pass, Oregon