Seeing anything that still exists from hundreds of years ago also makes me feel super connected to the past — like this graffiti stating the date (the day of the battle of Bunker Hill) in this old house in Massachusetts.
They should bring those back, be good for a little boost on a long day (couldn't be any worse for you than chugging a couple redbulls...)
They are the initials of the letter writer and the initials of the typist.