I don't remember signs like that on the taxi cabs I've seen in el estado de Oaxaca. There's usually just a sign on the top of the car (often a Nissan Tsuru) that says "TAXI." I can't even tell you whether they light up the signs when they're looking for passengers. Maybe. At night.
I'm not sure about buses, either. I've only taken one--it was from the coast up through the forest to Oaxaca de Juárez. At one point we stopped at a little spot by the side of road where the passengers could get out to buy cacahuates or tlayudas and use the toilets. Of course, two of the three toilets were out of service, and the lady ahead of me in line thought it was funny to stand next to them and say "Cobra me" when people would try the doors and find them locked.
And as far as engagement goes, I have had at least two marriage proposals from taxi drivers in Tsurus, but I didn't take either of them up on it.
Perhaps I've been *severely* overly influenced by Spanish ocupar. Now that I mention this fact to the world it might also only exist in certain dialects. Funny how I was so sure it was valid in English too.