Trying to identify an unknown current-source symbol
This is the figure referenced:

 

Also used on page 4:



That almost certainly means "trimmable" or "adjustable". 


If it had an arrow head on the cross bar it would imply an adjustment that was potentially user (or service person) changed. 
The T head usually means like a trim pot which is set for calibration purposes.


In this case it's inside the IC and you have no control over it (as far as I can see) - it may be LASER trimmed during manufacture? As you do not seem to be able to alter what it does it's not evident why they show it. 

Here's an example of the T head used to show a trimpot adjustment.



Similar here but the T head is shown next to the resistor