Wow, I just read two pages of opinions based on very sketchy information, at best. None of has enough information to pass judgement on anyone -- the original poster, or her neighbor. But people are doing it, anyway.
Mark had the best advice, and since he is a cop, it is informed advice.
Beyond that, I know nothing about the original poster, such as whether or not she is a busybody. And, I know nothing about the neighbor, who may or may not belong behind bars. I don't have enough information to pas those kinds of judgements.
The only informed comments I can make in response to the original post is, "Yes, trailers have VINs," and to do what Mark said, and don't try to be a detective. If you feel strongly that the trailer may be stolen, then report your suspicions to the police, and let them decide what to do.
CD