I thought “alto” meant “tall” in Spanish.
Google’s translation tool says alto = stop.
It also translates “tall” as “alto” (english to spanish).
As in English, a word in Spanish can have more than one meaning. The “alto” that means stop is, I think, related to the English word “halt.”
I was just going to guess that, becuase there don’t seem to be any other definitions of “alto” related to this one, according to my dictionary.
My hijack question would be why stop signs in some non-English-speaking countries say “stop”.
Yes, it comes from the same root as “halt”.
As to why the same sigh in Spain says “stop”, I can only guess one smashingly successful sales job by an early Anglo-American maker of traffic signs, faced with a surplus. ;D
The word for “to stop,” however, is parar, and a bus stop is a parada. Parado/a can also mean “standing up.”
This led to one of my friends making one of the funniest gaffes I have ever heard of when he first arrived in Panama. He told a bus load of people he had to get off because he had an erection.
When approaching your stop, it is customary to call out “Parada!” so the bus driver will know to let you off. My friend instead shouted out “Tengo parada!” Unfortunately this translates as “I have a stiffie!” (a “standing one”). He says he was surprised about how quick everyone was to let him off the bus. 
Some of the emergency stops on our machines at work say alto. Don’t even say stop.
So I wondered what the F the emergency stop had to do with music.
Obviously I don’t speak spanish.
When I was in Tijuana in '79 the stop signs said, “Coca-Cola.”
Or perhaps some kind of treaty in which all the signatories, say in Europe, agreed to have a standardized traffic signs, of which one sign would be the red octagon with the word STOP in white on it.
When I was in the Caribbean, I had a very good lunch prepared by a woman who held her infant while she cooked. I tried to tell her in my lousy Spanish that I liked the food and her baby was cute. She was bilingual, and she explained in excellent english that what I said was that I would enjoy eating her baby.
Hmmm… our official corporate standard is “Paro” or “Paro de Emergencia” for our E-Stops in Spanish – at least in Latin American Spanish. Maybe one day I’ll get to Valencia to see what they have there. I know that many of our Mexican engineers used to complain that the standard process language was Spanish Spanish instead of Mexican Spanish, and it drove them nuts.
Here in Colombia, stop signs say “PARE”, which translates to “STOP” in English.
Same here (Dominican Rep.).
Also *paro *means strike. Just so you know 
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Paro as in paro laboral or work stoppage.
Paro as in paro cardiaco or heart stoppage (attack).
And, hazme un paro and hazme el paro are slang for do me a favor or give me a hand etc…
Yeah, there was a paro nacional in Colombia in, I think, '98 or '99. Except that, in Bogota, everybody knew about it; in Barranquilla, everyone said, “What paro?”
Qu’hubo, Robcaro?
“pare” is also the 3rd. person singular present, or the 2nd. person familiar imperative, of “to give birth”
And Monty, I like my story better if you don’t mind ;). After all, the other major road signs are almost all non-verbal… (I love the one with the exclamation point. I want it to mean “Prepare to be surprised!”)