"almost nothing" would still equate to sever thousand dollars, probably over $100k. Not to mention future costs, a sticker would probably need to be replaced after a year at most, and a sign would cost significantly more. If you decide to just put them up and let them be there's a high likelihood of vandalism or damage that isn't attractive. All for signs that many people probably wouldn't notice. Again it just doesn't seem that letting people know the buttons do nothing is worth the money that it costs.