I need a symbol for safe work?

Question

I work in support for a construction company, we are making a test thing where you have to spot things that are unsafe in a picture and things that are very safe and mark them with a sticker, we have the unsafe ones all worked out but not the safe ones

What symbol would you use to show that people are doing something well and safely?

Answer 1

Green is the usual color for safety.  A green cross (as opposed to a red cross) is used by the American Society of Safety Engineers as a symbol for safety.   Perhaps a green triangle or green "S" would also be appropriate.  

Answer 2

Big yellow smiley face with safety goggles and hearing protection.  Smiley face also has two gloved hands giving the "buddy Jesus" sign.

Answer 3

A guy petting a walrus with a creamsicle in his hand.  

Answer 4

A thumbs up with a green background.

Answer 5

a worker with safety boots and a hard hat