Assume several scenarios:
1. A visitor from out of state was traveling, went to piss past a purple post. He/she has no idea, thinks that it is some kind of a decoration-bam, wham. Not exactly the same, but in Florida a nice Japanese student visitor was killed through the door when he was simply participating in Halloween celebration.
2. A local drunkard drove his truck past the "signs", went out to do #1 as well...bam..wham!
In both cases, those who do the shootin' would be dragged through the courts, charged with manslaughter, and even IF they prevail, it is DEFINITELY not worth it if lives were not REALLY in danger.
Protect the property? Well, bears and rabbits shit on your property daily with no recourse..well maybe they got shot too from time to time, which is fine.
Additionally, assume scenario #2 happened. If the guy/gal who was shot in this scenario was also local, you would NEVER be safe.
His or her relatives...they got 'them telescope rifles as well, don't ya think?
Again, shooting mere trespassers is not legal in any case. Urban legends, old wives tales and the fact that you would probably get away with it if you weren't completely stupid notwithstanding. It's merely supposed to be a no trespassing sign. Though I do agree that it's really not very good from the point of view of someone who has never heard of this totally non-obvious custom.
By the way, I do recall reading that there were other parts to the Japanese student (though I think that was Texas) that were not being reported (quelle surprise) which, while not making the event particularly better, do shine a different light on things.
If I'm not wrong Texas has a law that let's you kill anyone entering your property uninvited after dark.
If I recall correctly the couple that shot the Japanese student did shout "freeze" several times and he did not stop, and it was after dark.
Don't know that story. It sounds tragic.
However, if you travel, be aware of the "habits" in different areas.
And in some parts of the USA, you just don't enter people's property uninvited, no exception.