I don't know the exact name of it, but its purpose is to keep a calf from getting milk from its mother. I believe this was to ween the calf, which was perhaps destined to become veal. My mom has a bunch of old farm equipment on her walls, and one of these is on there.

I've seen this concept before here: http://spamusement.com/

Jesus refers to himself symbolically as a hen in Luke 13:34. This is depicted artistically in the Dominus Flevit church in Jerusalem: http://www.flickr.com/photos/32829981@N00/416773088/

But this is the first time I've ever heard of the rooster symbol, though it is easily derived from the hen I suppose... and it all leads nicely to Easter eggs!