Panthers are known to lick branches as a way of smelling/identifying their terroritory, mine does it all the time. If you are leaving the blinds open, he probably sees a tree that is swaying and wants to go to it. My melleri did the same thing when I left the blinds opened and would nose rub. I know you have good intentions and want the cham to see the outside world, but if it is stressing him out by wanting to "go there" it would be best to not show him the outside. I would move his cage to a corner of the room and set up an exercise area in front of the window. That way during the day he will spend his time basking and absorbing the UVB and in the evening you could let him out to climb around.