@Steve - Driveway vs. Road
It's apparently shared with other residents, so it's not a driveway at least in so far as we understand the term here in the UK. However they do speak a different language in the US, but when reading stories from the US we tend to read them as if they were written in English.
That, however, is not my point. This is:
Even if there was a sign I wouldn't assume, on seeing it, that it had any standing in law. I don't know exactly how the law works or people operate over there. Over here, however, such signs are quite common and are often misleading. A couple of hundred yards from my house there is a cul de sac that bears a sign reading PRIVATE ROAD NO PUBLIC ACCESS. However a quick check of public records shows the road to have been adopted by the council about thirty years ago. As such it can not be a private road. Some people want to feel they live in private gated communities when they don't. It seems to give them a feeling of power over the great unwashed, but to my mind there is a simple way to deal with these idiots. The local council, royal mail, etc. should simply stop at the sign and refuse to go further. How would they feel if their post was dumped at the end of the street, the bin men wouldn't collect their bins, the council wouldn't repair the road, the water mains became their responsibility from the main road and so on?
Within a couple of miles of here there are half a dozen similar examples, indeed such signs are so common that unless they are official looking local authority signs I assume them to be illegitimate.
Were I in Google's shoes I would set my navigation softare up using the definitive map (or whatever the US equivalent happens to be) and then there could be no reasonable argument.
BTW in English law I thought there had to be a clear boundary for trespass to be deemed to have taken place, even then the intruder must be asked to leave. Otherwise every uninvited caller to knock on my door would be guilty of trespass. The sign "Tresapassers Will Be Prosecuted" does not mean (even in Winnie the Pooh) that by being on the land you are trespassing, it means that if you trespass on the land you will be prosecuted. A subtle but important difference.