Obviously, I face the whole "sit or squat" issue from the Western,sitting, perspective. However, if you reverse roles, then it is pretty easy to imagine how a person that has grown up knowing only squat toilets might react when faced with a a "sitter" for the first time. Luckily, there are many signs designed to help first timers learn what to do.
Sit, Don't Squat
This sign was in a public restroom on the UM campus.
Keep The Restrooms Clean
This sign, from the public restroom in Sungei Wang Mall in Bukit Bintang, contains a list of nine things you should avoid doing in order to keep the public restroom clean.
You should avoid (1)trowing cigarette butts into the turinal, (2) throwing trash in the toilet, and (3) taking water from the cistern.
Also, you should avoid (4) scribbling graffiti on the wall, (5) spitting on the floor, and (6) squatting on the toilet seat.
Finally, you should never (7) wash vegetables in the toilet basin, (8) use your foot to flush, or (9) wash your legs in the toilet basin.
Signs for Westerners
To be fair, I have seen signs aimed at Westerners in public restrooms as well. For example, at Changi Airport in Singapore the stalls containing squat toilets have a sign on the door that says something like "be aware of the open hole inside". It is easy to imagine that some jet-lagged American has rushed into the stall and fallen in. I will try to take a photo next time I pass through Singapore (of the sign, not of some unfortunate tourist).