Interesting question with many points of view. I do alot of bushwhacking in western MA that often requires crossing private and sometimes posted land. Clearly the law is not in my favor while crossing legaly post land but sometimes I do it anyway. Many owners post their land because if they need to restrict access to people who abuse their property the police won't respond if the land is not posted and have little legal authority to do anything other than to ask the abusers to leave. Most do not mind people(using common sense, like not going into private hunting preserves) just passing through their land and none would know I've been there unless they see me. As we all know, it only takes one inconsiderate person to ruin it for everybody and posting land can often times be an inexpensive way of warding off the rude and unruly. I'm willing to gracefully accept the consequences if some land owner does indeed want me off his land and has me arrested. Its the cost of having many vulnerable places preserved. However, more related to your paddling experience, I can see where some rights need to be clear and enforcable when it comes to access of public lands and waterways. Cape Cod has many public access points to the beach that are intentionally obscured by abutting property owners with the intent of denying public access. There are even some instances of people illegally posting such points, and your paddling trip inquiry may also be another example of property owners and abutters claiming or honestly thinking they have rights that in reality they do not have. I would be interested in knowing what the true intent of the property owner in question is and how vigilently they enforce their postings and if the postings meet the requirements of a legal posting. Of course if their desire is to keep destructive nusance people out it would be counter productive to publicly say anything other than keep out. This is an old discussion and argument. Some would say that you should just use the route you like and share your experience with only a few trusted friends. I get all sorts of grief from my hiking buddys when I want to post a trip report on some Adirondack bushwhack we've done on public land. I get no sympathy when I point out that I discovered the area by reading other peoples posts. They want it to themselves and do not trust others not to trash it. I say the more people who know of a great area, or trip route, the more political clout there is to protect such areas and access rights by law. They tell me that my point of view is idealistic and has no actual relevance to what actually goes on in the real world and they have many good examples to prove their point. I reply, "Have you ever heard of the Adirondack Park"