The simple facts are, the sun is coming from behind him, not in front like you think it is.
Look at the shadows on his right arm for proof of that fact. As far as the holding of the sign, at that height and angle, it is unnatural for a human hand to hold anything in that awkward position and would appear to be out of proportion as you noticed, but it can be done for short periods of time.
Then the face of the sign would be in shadow, not direct sun.