It's been quite a while but I seem to recall the signal was somewhat like this:
While making the 'OK' sign with your left hand (but only done in countries that find that gesture unoffensive) firmly press your right index finger to your pursed lips. Upon making visual connection with said ground staffer, puff one's cheeks (ala Dizzy Gillespie)....
Or at least, that's what i recall...
Air-Geko
(behaving as if this is Jet Blast)...