Oddly enough I could argue the opposite. The need for those warnings is an acknowledgement by the owner that they do not intend to properly secure their property, and are instead asking people not to take advantage of that fact.
And there's the fact that the owner went through the trouble of creating that sign without bothering to simply secure their property. Another acknowledgement that leaving property unsecured in public is not reasonable.
And there's the fact that the owner went through the trouble of creating that sign without bothering to simply secure their property. Another acknowledgement that leaving property unsecured in public is not reasonable.