Question: What the flip!! What does it mean when someone signs their name (on the computer) with a "J" after it? 

Answer: It means "Jammin" or "Cool". Like Cool Mo D or Jammin Jam master J. You could also sign W for Wiggin or R for Rad or Radical or P for Pertty Good. Got anymore questions concerning this matter, just ask.
This question from the Yahoo Q&A forum is categorized in the topic: Family & Relationships