Someone stuck two 1-cent proprietary stamps on a legal-sized envelope instead of using actual postage stamps.
He or she seems to have intentionally left their return address off of the envelope (the back side is blank). Maybe this was just a coincidence.
The stamps were cancelled on May 2, 1920, but a clerk noticed the incorrect stamps and sent a note to Mr. Jackson, requesting a two cent stamp in order for him to receive his mail.
He must have not been terribly enthusiastic about this item, as it took him a month to get around to coming up with a two cent stamp.
Plus he had to pay to have the stamp mailed to the Gary post office.
The two cent Washington stamp was duly received, attached to the envelope, and then cancelled on June 3, 1920.
Mr. Jackson marked the envelope as received on June 7, 1920.
One can only imagine the conversation that might have then taken place between Mr. Jackson and the sender...
Jim
