The sign is not joking. Red wing blackbirds hang around these wetland retaining ponds in Tumwater and dive bomb people. A few years ago one of those little devils actually drew blood from the top of my cranium!
I blame Alfred Hitchcock for giving these birds such fowl ideas.
Sometimes a black bird will be looking as if it is poised for attack, but it turns out to just be a crow. No caws for alarm.