That is heartless and tremendously funny at the same time.
I grew up with cats, my wife loves 'em. I could take 'em or leave 'em at this point in my life. My wife has three cats...I like one of 'em but would like to use one of 'em for target practice. So a dead cat is a good cat sometimes.
Not sure I would be brave enough to make a sign like that for somebody's pet though.
Still funny...in a strange, darkly humorous way.