Going through `/etc/mime.types` this afternoon, I discovered a delightful little gem:
The only reference to it I could find was a 1997 request for its MIME application. Of interest:
MIME subtype name : Vendor Tree - vnd.3M.Post-it-Notes Applications which use this media : Post-it Software Notes v1.5+
Now that I think of it, my old man bought and used this with his Windows NT machines back in the day. They were rather cute.
Other information was decidely less helpful:
Required parameters : 3M Confidential Optional parameters : 3M Confidential Encoding considerations : 3M Confidential Security considerations : Independent evaluation impossible due to specification non-disclosure.