Notice the letter was sent on April 15, 2016, typically the 105th day of the year, but this year the 106th. It contained a picture of Hillary Clinton with some dates and words written in yellow highlighter.
If you don't recognize that face, it is the young Hillary Clinton.
In yellow highlighter, the person has written the following information:
AD 802, 701
They also wrote the words, "When
If anyone wants to take a stab, cheers to you. I'll do some thinking later.
It appears the letter came from the Washington D.C. area.