This usage is derived from code language used by Freemasons, because of their strong association with the carpenter's square device. It has basically entered the common vernacular at this point, but in combination with other symbology, it may signal that you are seeing a conversation between Freemasons.
Ha! I’ve used that phraseology for yeeears and only just learned about the Masonic connection. I think it’s safe to say that it has fully entered the common vernacular.