Despite the LOTG implying that no other signals are permitted, I'm sure we've all seen referees use a "throw in" gesture to clarify it is a throw - either when in the corner and there's a possibility of a corner/GK, or elsewhere on the sidelines when there is an appeal for a FK that isn't given, but the whistle is needed regardless as the ball is only just out. And also, to clarify that a foul throw is the decision and play should be restarted with a throw, rather than a foul for a push etc in the drop zone.
Don't try to be too specific with the height/angle of a signal - no player will know the difference and you'll just confuse people if you assume they will. Communicate with your voice and if a directional signal is needed, this can be before or after the clarifying throw-in signal, just don't try and do both at the same time!