BINGO. "DADDY"
A child this age doesn't just accidentally have their hand on their forehead this way. There's specific placement-- it's not a natural hand position for a child this age, unless practiced.
So, whose account was this picture found on? And when was it taken?
Since Caylee did not have a father to speak of she was probably signing 'grandfather', but then again, who knows what she called George.
This is a very deliberate hand gesture and it looks like she had practiced.