If the MWCA doesn't care enough to post a conforming sign then why bother getting upset over it. H&H, your instructor was wrong. The law was written with idea that the signs could just be ignored as long as you carry concealed. This is why there is the two step process with the clear standard of signage and/or a verbal warning and then refusing a verbal trespass order before you are violation of the law.
Furthermore with section of the law which restricts landlords from posting businesses, one could argue that MWCA is prohibited by law from posting as they become landlord for the day.