The ultimate passive aggressive move would be if Steve wrote the sign and then blogged it in order to be doubly passive aggressive--outing his co-workers as being filthy pigs, undeserving of life
I had a housemate a number of years ago who would put my dishes in the garbage can if I left them in the sink too long. Not sure if that's passive or aggressive, or both or neither, but he only had to do it a couple times before I got into the habit of cleaning up after myself...
Wait.
Nevermind.