What activity does this "don't do this in a Thai taxi" image refer to?

Question

The recent question Do taxi colors matter in Thailand? links to Amazing Planet's March 14, 2014 Bangkok’s Multi-Colored Taxis which includes a reproduction of the image shown and credited below.

I think I know what all of these "don'ts" refer to except the one on the far left, shown separately cropped, zooomed and sharpened.

Question: What activity does this "don't do this in a Thai taxi" image refer to?

source: Adam Bowers' 2011 Flickr photo "forbidden taxi" https://www.flickr.com/photos/ill_dawg/6807960308/in/photostream/

Answer 1

From Reddit, the symbol represents a water buffalo, and the Thai word for buffalo also means idiot, so the sign means no idiot / don't be an idiot. Ask the taxi driver if that sign means that the car is a self-driving car.