Most signs have a sort of universality about them: the male/female symbols that denote toilets, the non-smoking sign, etc are instantly recognisable anywhere in the world.
But this sign took me some time to figure out.

[Image from http://www.ling.su.se/staff/evali/simuk.htm]
I first saw it while waiting in line to get through Immigration at Jackson International Airport, and wondered for a few minutes why they would put up a sign specifically forbidding grenades!
Once outside the airport, it dawned on me that the red spit marks everywhere and the sign were both a tribute to betel nut.
Betel nut (known as buai locally) makes it’s presence felt everywhere: people selling it on the footpath, signs forbidding people to sell it on the footpath, signs forbidding people to chew (and spit) betel nut, ugly red splashes all over the road and footpath. In some places the red stain is not just the odd splash but a solid red blanket covering huge areas of footpath and wall.