"Good to know! You don't have to legally stop at all stop signs"
I just don't even.. Before I even get into how this isn't remotely true, Generally if a stop sign is placed somewhere it's for a good reason - it's there so that people stop and are aware of possible on coming traffic. Private or public roads, it doesn't matter, it's a visual guide to let you know stopping and checking for traffic in that spot is probably a good idea.
But on to why this isn't remotely true. As the pin states, it's more and more common in commercial and residential areas built by developers to place stop signs and other road markers. But this doesn't make them not legally binding. In fact in a lot or areas the developers MUST place proper road signs in areas before the city will even recognize them as streets. On top of that, in the majority of states here in the US, the police DO have jurisdiction on private property - so if you run a stop sign in the mall parking lot, a police officer CAN pull you over for reckless driving. Not only that, but if you run a stop sign and get in an accident, insurance companies couldn't care less if it was a 'real' stop sign or not. You will still be legally at fault for ignoring street signs and markings. In fact there is a great write up on this over at Quick and Dirty Tips about signs posted on private property.
But lets also take a look at the image here and think about how they say proves a sign is not a 'real' legal binding sign. It's a sticker on the back of the sign. So in order to know if a sign is real or not, you have to STOP your car, get out, and look at the back of the sign. Also if a mere sticker is all it takes, then the majority of stop signs I've checked out in my city are apparently not legally binding. (or just old or stickerless) What happens if someone decides to pull that sticker off? or fades and washes away with time?
All in all this is just asinine, not true, and a bad idea.