That is creepy, they have your name but they do not sign their full name and they use a post office box number instead of their personal address. If they truly believed what they wrote they wouldn't have a problem with any Tom, Dick or Harriet having their personal information to be sent on to just anybody.
To be fair, I have received 3 of these letters. Each of them had their entire name and home address. One of them was handwritten, the other two were printed.
I decided to reply to 2 out of the three, which i'm sure shocked them to receive an answer.