In some states it is not illegal UNLESS there is a posted "No Trespassing" sign. Otherwise it just helps cases a lot more when there is trespassing. The defense has no way to argue out of it.

Whenever I see those, I just take it to mean that there is either a large angry dog or a large angry man with a gun on the other side, so it just reiterates it for me. It is a bit redundant though. We should all put signs on our front doors that say, "No Murdering" or "Thou shalt not envy thy neighbor's wife"

Not always. When your out in a state park a no trespassing sign lets you know you are starting to encroach on private property. You can't always rely on fences. They are sometimes non existent or falling apart.

They are useless in a civil case, but not for a criminal case. In order to be guilty of criminal trespass, you must have the intent to trespass. In order to prove intent, you basically need to prove that the person knew they were trespassing. In areas where it is not clear, the sign will make it clear.

Generally, before a person can be arrested for trespassing, the person must be given a warning. having a posted no trespassing sign covers that area. It also makes a better case in court, if the signs are posted. If i receive a trespassing call, in my presence, i have the complainant verbally give the person a warning. if the person still refuses to leave, he is arrested.

apparently they're still necessary because some people just don't get it

How will people know that trespassing is in effect without a warning sign of some kind. I don't think you can be charged with trespassing if it ain't posted.

The sign is not at all redundant. Believe it or not, some people welcome others to use and appreciate their property, especially when there's hiking paths and streams and beautiful scenery. Not everyone in the universe is hostile. Living in America, I've always been impressed by how people are consumed with ownership, possession, and isolation. It's almost as if we must eradicate all people from a place, wall it off to guard against every possible footstep, before we can relax and consider a place mine, mine, all mine, thank goodness I finally have a place in the world, it's mine! This attitude of automatic possession is very strange. If we could attach ownership to clouds, I bet people would go crazy to grab as many clouds as they can, and shove everyone else away from them. Or charge them admission to see their cloud in the sky. Even at a beautiful art museum I hear people saying "I wonder how much that costs... how much does THAT cost.. That's so beautiful, I wish I could own that one. It's so nice, I wish it was mine. Gosh, I could put that in MY living room." Beautiful museums belong in a museum. Hiking in Nature, belongs in Nature. I, for one, am really grateful the federal government hasn't sold off and barricaded all the land just yet. And if I'm playing basketball in the street, I hope it's never a crime to fetch the ball when it bounces into someone's yard. Or to knock on someone's door to borrow a cup of sugar. What kind of robots are we turning into?

No, I don't think so. Not all properties are off-limits. Public property like parks, for instance. Private property like vacation resorts. Most land boundaries have no clear marker, and this creates one. It also states the owner's intent that you are not welcome on the land. Not everyone is upset if you walk on their property.

You have to post your land if you do not want trespassers and hunters on it. Sometimes they will look for areas that are not posted and enter anyway. Not cool!