I went back in the daytime, and the billboard is back to normal.
I **know** that it was gone last night, and I have witnesses but not PICTURES. :(
This afternoon, I talked with a guy who works in the costume store in the building under the billboard.
He says that the billboard WAS in fact vandalized, but that the billboard people were apparently prepared for such an eventuality, and fixed it ASAP.
NEXT time, I will have a digital camera with me.