It is the average stack divided by the big blind - or in simple terms how many big blinds the average stack has in the tournament.
one of the most important factors you should monitor during your tourney's to ensure the structure is working. If you look at this figure during the middle stages of deep-stack poker tourneys you will almost likely see that the average is a short stack which causes an 'elastic band' effect with rapid eliminations at key stages of the tourney, rather than a smooth string of eliminations.
With regards to your question I am not sure it is possible mickle, there is no token and it would require a mathematical equation to formulate a display for this information. Is this really something you would want to show your players anyway? I use it constantly to monitor the success of the structure in use but would never display this information to the players as it would likely be negative to the best interests of the game.
Stu