I found this in my grandparents' papers, along with its letter from the postmaster (a family friend). I'm wondering if it has value for anyone....
How about you or another family member?
My father, eventually a postmaster himself, collected first day covers (envelopes with the stamp used being used on the very first day it was being officially sold by the USPOD). While I too am a stamp collector, I have little interest in first day covers of that era which have little monetary value similar to your item. EXCEPT they have great value to me as they document the various addresses at with I lived throughout the City of Berkeley CA between being brought home from the Berkeley hospital until the house in an adjoining city was purchased a couple of years later with an address I can remember and at which my parents were still living when they each passed from old age. I moved more arriving at the house than my two moves leaving the house.