Opposites of RSVP
Solution 1:
You should not be using initialisms that no one will recognize and few will figure out. Instead you should explicitly state what you do or do not require or expect of your correspondents as a matter of courtesy.
Solution 2:
Just because no one recognized WYSIWYG or WTF, that doesn't mean new acronyms are illegal and shouldn't be created! May I suggest the acronyms DNR (do-not-reply/respond) and a more polite NRN (no-response-necessary); or RIN (respond/reply-if-necessary)?