Do you know why this worker wears a healmet with a green cross? Is this EMT emoji? No, the emoji is named “construction worker.” So, what does the green cross mean?
The origin of the green cross is: Flag of safety, designed by Toshifumi Gamō as the symbol of the governmental "safety week" campaign. The symbol of green cross is common in Japan and you can easily find at Google Images. The frequent word「安全第一」 means “safety first.”
Drawing green cross in a helmet is the easiest way for Japanese to connote the person is a construction worker. Some emoji have such culture-specific symbols.