I am told that there are hand signals for the carros.. both for the drivers and the passangers.. Something like Fingers pointed down for going straight on up on Duarte.. Held in the air for going across the bridge.. complicated stuff. But this is the really Secret stuff. You get a printed guidebook, The secret decoder ring. The handshake. All that secret stuff. But the meetings on how to join.. and get that info.. well., they are secret.
But the info on finding a car with the front seat empty and paying double.. that is Not secret and makes for a perfect cab ride.
When you screw up a couple of times not understanding the signs and end up in bad neighborhoods, you learn very fast
The signals depend a lot on where you are, since they are mainly meant to show the passengers which route the carro is taking (e.g. a finger pointing to the right en la San Vicente on the way to Las Americas means that the carro is going to get on Las Americas and cross the bridge, while a finger straight up in the air means that he will cross Las Americas and go down towards 25 de Febrero).
So the signs are place bound, from my experiences, meaning that you have to learn what they mean on every single place where there are more than two routes operating. Number of available seats is a lot more understandable, and the waving sign towards the ground is just a tic, I suppose.
Best part of walking the streets is to watch the reactions when our 1.5 year old son decisively waves his little finger to show cobradores and carro p?blico drivers that we are not interested in boarding their vehicle.