I got this idea from recent news stories about messages in bottles being found on the shores of various places in the world after many years at sea. I combine that concept with something I and a friend did as kids - we filled party balloons with homemade H2 with an attached, pre-addressed questionnaire post card in a plastic sandwich bag and a length of aluminum foil for visibility during a balloon's eventual descent - you can see one flashing in the sky for an amazing distance on a sunny day, long after the balloon would otherwise be invisible. We received as I recall about five returned cards, all from several US states away (~300 miles) except for one which was found on a New Jersey beach about 1000 miles from its launch point.
I ask here for brainstorming about an Arduino environment developed, lowest possible cost, low-power, solar powered (with recharging battery) ATtiny system to act as an intelligent message in a bottle designator. While floating at sea, it would not attract any attention to itself and would simply keep the long-shelf-life battery (or cell) charged whenever necessary during daylight hours. When it senses that it has come to rest on a beach, it would wait for nightfall and set off a slow repetition rate LED strobe in the early hours of the evening, never using more battery power than could be restored in a few days by solar recharging. A pre-addressed post card explanation and questionnaire (ex., "when and where did you find this?") would be included in the bottle.
I have no idea about the odds of something like this ever being found after sea launch, so it would need to be as inexpensive as possible to make it worthwhile. It wouldn't be a mass effort by one individual, it would be a large number of individuals building (or buying one pre-made) and launching on their own.