In sign language (A.S.L), initialized signs are these signs that are initialized with a given letter in order to disambiguate. A common example is the case of the words dentist and water, in one case we initialize with the sign for the letter D over the mouth, while in the other case we initialize with the sign for the letter W. There are cases where the second letter may be used if the two first ones coincide.
So, a sign that will be not an acceptable initialized sign is a sign that is non-ambiguous, and in the given options, the one that meets this requirement is the sign for father. (tapping your thumb twice in your forehead).
