These metal sculptures were at a bar-b-que place in Sonoma I went to last week. The saying When pigs can fly must have meaning behind why the owner chose this image to represent his bar-b-que joint. The pigs stood on top of trailers used to cater food around the area.
The meaning behind that saying is "it will never happen".
Maybe he knows his bar-b-que isn't all that great. I've had better.