Varies on state. Here is what
the law states in Texas, which can be very different from other states.
The purple paint and the sign give the "notice" as prescribed by law. No warning needed before the sheriff gets called.
As for when to bring out the firepower, this is a good
guide.Believe it or not, Texas isn't that bad. However, I've had stories because Austin is the fastest growing city in the US (as per Forbes), so with people moving in, statistically, problems and crime follow.
I can understand protecting one's property because there are plenty of neer' do wells out there who are looking to get access to stuff (and this is not intended to be flame against anyone here.)
However I've become lazy in life, and it is a lot easier for me to sign a police report, hand the sheriff over some footage from my CCTV system, then sign an insurance claim... than it is to fill out a booking form at the county jail due to an unauthorized firearm discharge within city limits, or even worse, arraignment forms for other firearms offenses. Nothing in my place is worth spending months dealing with criminal courts and juries, because if I'm out and working, most stuff can be replaced with an insurance check or at worst, a few paychecks.
Now, a burglary of a habitation is a different thing, of course.