In my case it comes from having to actually hand write or manually type notes and letters on real paper for the first 45 years I could read and write. A habit that carried over to posting on a forum like this one.
I always signed even the briefest note to another person my whole life and it just stayed with me when I starting posting here on the Rx about 6 years ago. Can't help it and now it is to late 48,000 wil's later.
wil..