We tend to think of certain common icons as fixed and standardized, but in fact, if you pay attention, you start to notice that very few of them really are. I mean, how could they be? A logo for a company (the mark could be seen as an icon in a sense) is central to its brand identity. Therefore, they have vector art files for it and usage guidelines, etc. It is exact and must never be tinkered with or they risk diluting the brand. Icons (visual symbols, pictographs,  whatever) in the world are quite different. Something that I find really fun about them is the endless variation. Its like they are all slightly distorted copies of an original that has long since been lost.

One of my favorite examples is the wet floor sign. I started amassing a small collection:

I personally think this guy is break dancing.
This might be the most elegant I have seen. The designer used a common “slipping man” symbol, added waves to indicate water and the universal exclamation mark for caution. No language needed.
This guy landed on his bum. Could also work for Slip-N-Slide.
This one is really common, but it always seemed like an odd way to fall.
Every now and again you see some interesting hand made modifications to a sign. In this one they seem to be adapting the wet floor sign to also mean “working”. The third eye on the top must be mean “look out” or perhaps warding off evil spirits.
A combination of the bent knee and the Slip-N-Slide
Found online: Sliding or about to lay down for a nap.
Found online: Adding the little puddle isn’t a bad idea either. Note the extra effort on the shoes and hands too.

Of course, this is just one example. This post could go on and on. There are so many to pay attention to:male/female bathroom, handicapped, elevator door open/close, walk/don’t walk characters (I have small collection of those too), even the arrows on highway signs often differ by states.