Does it mean something in particular when emails have capital-letter "J"s that appear seemingly randomly?

For example: 

I think it does lend a sense of closure. And you got thrown in a pool for it! J I definitely believe it works as is...

Is this a typo?  An email glitch thingy?  Or...? 

I ask this because I've exchanged several emails with this person.  And not all, but many of the notes have a random "J."