Just because the three types famously go together, and so if two of them are used for a particular purpose (links), it seems reasonable to also include the third . One of these would definitely indicate a pedestrian trying to do something, and others should be careful not to interfere.

There is a known problem with large carnivorous animals, which is that they are generally difficult to tame and keep tamed. Well, there was a book I read long ago by Arthur C Clarke, "Dolphin Island", that described a technique for inserting electrodes into the pain centers of an animal's brain. When it misbehaves, press a button to remotely give it some pain, thereby telling the animal it should not misbehave in that particular manner. According to Clarke, the technique was actually tested and works well.
-- Vernon, Mar 09 2016

Lions Seeing_20Eye_20Lion
As mentioned in the main text. [Vernon, Mar 09 2016]

Bears Guide_20bears
As mentioned in the main text. [Vernon, Mar 09 2016]

random, halfbakery