If you happen to be visiting NYC, there's a building at 42nd and 7th ave... very close to Times Square, that has a bunch of Z billboards running around it.

I didn't walk all the way around the building, but there were at least 6 different ones. They appear to be all the same ones you see around the country on billboards and buildings, but all in one place. There was at least one I had not seen before. Pretty cool...