Where a driving licence which is expressed as not having effect until it is signed by the grantee is granted -
(a) it shall be the duty of the grantee forthwith to sign his name on the licence in the place indicated in that behalf therein,
(b) if the grantee fails so to sing the licence, he shall not, for the purposes of this Part of this Act, be regarded as not being the holder of the licence merely by reason of such failure.