My workplace is bad about proofreading signs and notifications before they get out to the public.
1) this was about 10 years ago. Some heavy equipment got installed near a facility so as a warning the roadways were marked "HIGH ИOISE AREA" by spray painting through a template. Problem is, when the template was made, no one noticed that the "N" was backwards. For the years until it was disestablished, we jokingly called that area "Nine Inch Иoise."
2) around the same time frame, there was a high number of near-misses as bikes and trucks were coming hot around corners without heed for pedestrians. Safety division decided to put up warning signs at some of the worst blind spots. "CAUTION: YEILD TO PEDESTRIANS" Well one Friday we were leaving work and we saw that on the one sign closest to our shop someone had written in Sharpie "I before E except after C!" A week or two later the signs disappeared, and were eventually replaced with the correct spelling.
This one is new, as of yesterday in fact! 3) Some spots in one of the parking lots just got sectioned off for reserved parking. In each commandeered space is a sign. "RESERVED PARKING. DO NOT REMOVED SIGN WITHOUT PRIOR AUTHORIZATION."