If I would pass a sign talking about men shaving or not, I would not care, it doesnt apply to me. If you care it means its touching you somewhere deep inside. Don’t try to brush it off.
If you think 4 inches is ridiculous, you shouldnt care.
BS”D
I completely agree. The OP had a good point regarding posting signs on private property (Gezaila, just like any other use of someone elses property without permission, such as hanging your stuff on his tree, or storing your bike in his shed without permission). The “four inches” is so ridiculous that it means nothing to me.
That other Jews say these things (and mean it), well, I just don’t have the same religion as they do (shrug). Judaism depends on who your mother was, not by claiming that you are practicing, or creating halacha. If it was, the Karaim and the Reform would both be frum. To me, it is no different than saying one must take an apple together with the Arba Minim.
Of course, if you would ask the learned people, they would tell you it is a geder, a siyag, or a general idea. It is the Hamon Am that are Amei Ha’aretz (just like it was in Europe), and make the broad statements.
Unless you actually might think the “four inches” could be correct, why does it bother you any more than someone who tells you your Esrog should be a plum?