Sure Chuck; your method would work at least as well, at deserted aerodromes or in airplanes where you can see the prop(s) from the cockpit.
On the other hand, it's best to call out when attempting to start 'blind' airplanes at busy airports (there have been incidents in which ground crew have attempted to rig up Harvards and similar airplanes for towing, not knowing that there was a pilot about to start up).