I’ve seen this in some posts from time to time.
What does it mean?
And, no, I don’t have any references at hand.
You write it at the title of you post. It means “No message”.
Interchangeable with nt, No Text.
“No! You can’t take my medicine, I need every brain cell blazing to outwit my invisible enemies!”
And IIRC? What’s that?
IIRC–“if I remember correctly.”
No, no, no. “nm” means you’re writing about New Mexico, or a National Monument. If you wanted to write about a National Monument in New Mexico, you’d use “nmnm”.
“That’s entertainment!” —Vlad the Impaler
And all this time I thought nm stood for ‘not much’!
“I may be crazy, but at least I’m not as crazy as you.”-- Calvin and Hobbes
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if it is n/m then it’s never mind. 
IIRC is If I Recall Correctly
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“Meat flaps, yellow!” - DrainBead, naked co-ed Twister chat
O p a l C a t
www.opalcat.com
To rich Texans it stands for Neiman-Marcus.