Nemo writes little scripts to do things. They have outputs to say what they're up to.
He's slowly over the years come to the convention of starting each line of output with a character to signify relevance.
Here is, roughly, how it works
# Headings. ie, new major stage has in progress has been started. : Info: Basic status output of stuff ! Alert/warning information - Related subinfo to the previous info or alert. + debug info