i do this all the time, so i've seen all kinds of reactions.
First of all, i've never used a grocery bag to dispose of them in a public place, i just fold them up and put them in the garbage bin in the hotel room. I have pooped a few times, and i will wrap those up in another garbage bag, so i see your point.
I also leave my diapers out on the dresser or someplace that is totally obvious. I always take a mental picture of how the diapers were sitting before i left in the morning to compare with what they look like that evening. If the stack is knocked over in the morning when i leave, a lot of the times the housekeepers will straighten up the stack or move them around to clean the room.
i have had a few house keepers look at me funny, but the vast majority are super nice and have probably seen it all before.
iluvdps