what is J. ? ? ?

i’m seeing an emergent trend of people from work ending emails, or ending their parentheticals within emails, with J. or simply, J

eg. Coldcake fans, remember this site is totally suitable for work J

is it some new form of smiley that i am not recognizing? what is it? I really dont understand and i’m afraid i’ll look horribly uncool for not knowing if i have to ask. (not really J.)