my mother brought up human psycology about a sign that the hotel put up, 'Do not fish on the balcony' and how indirectly, it put the idea into the other not-so-creative (or naughty) tourists and so they try.
it reminded me about the time i was form 1 in a new school. the headmaster gathered all the guys and talked to us about manners and etiquette, discipline... you know those stuff. and he proceed on to telling us not to do this foul hand sign or do this other foul hand sign. so, from knowing only 1 'type', i ended up expanding my knowledge with an extra 5 or 6 'types' (different races have different type of foul hand signs, for your info).
so, another indirect case of learning.
note: don't ask me for the signs.