Hey, it looks like a temperature measurer.
The colder it gets the more resistance it give and how warm it is the les resistance there is.
My guess is Q1 on the schematic. Possibly a 2N222 transistor not required in most cases?
A better picture of the numbers on it would be helpful I think.
That is a transistor - and it is referenced in the assembly instructions in this text:
(Note: There is also a transistor included in the package, which is optional. It lets you program the ArduStation wirelessly (without the FTDI cable) using Arduino. For that you need to solder the 2n2222 transistor on the board and follow the instructions for Xbee Arduino programming given here)
Thank Heino ;-)