It's only an abbreviation meaning "no reply/response needed".
So, what do I mean when I say, "NRN"? It simply means that if you're thinking about replying to my message or comment because you think or feel that I may feel bad about you not responding, then you don't have to worry. We're cool ;')
But if you really feel compelled, you're very welcome. We are cool ;')
Sometimes, however, I would very much like to "hear" a response from you. Mostly, I want people to think and analyze, I want them to see what's possible, I want them to be open minded, all without losing ethics and morality, and your response will let me see what you thought about what I said. Or if you thought about it at all.
Thank you ;')