Hello Pablo,
you can use the property IconName of the GUILabel object.
From the help: "If the object has been assigned an icon, then this property is the name of the icon, otherwise it is an empty string."
Try this:
MsgBox session.findbyid("wnd[0]/usr/lbl[3,14]").IconName
It should show S_TL_G for the green, S_TL_Y for the yellow or S_TL_R for the red traffic light.
Check it out with the TAC SE16, the table ICON and the Scripting Tracker.
Hope it helps, let us know.
Cheers
Stefan