He looks to be in the position of "Port Arms!" Though that is only used for ceremonial purposes, and he would be at the position of attention and/or in some sort of formation.
A low ready position would be more accurate portrayal of a combat ready soldier.
For a disciplined combat ready soldier with active ammunition, they would never place the barrel of the weapon towards the sky, in case of misfire.
So it really depends on the situation as to how a weapon is carried. That of course only applies to our universe.
EDIT:
As a caveat I forgot to mention longer weapons like muskets wouldn't be pointed down towards the ground while in movement for fear of catching the weapon barrel on the environment.
