[zaroth]

No, they put the signs on every building everywhere because it’s cheaper than not putting them up and possibly getting fined $2,500 for everyone who ever walked inside.

It’s impossible to construct a building which would not contain some element which would trigger the legal requirement of posting the sign.

The sign conveys you absolutely no information. Look closer and you will see they are posted on every commercial building run by someone smart enough to know to post them. The more entertaining places I’ve seen them is grocery stores and preschools.