However do remember what Metro means, it is short for Metropolitan, as in Dublin Metropolitan Area, using the term for just one particular type of rail based public transport is actually a misrepresentation of the term. Using Metro as a term for all public transport options in a Metropolitan area is actually more accurate.
It does convey a certain type of transport in its meaning in the vast bulk of cities in which it's used. LA is really an exception to the rule here. I would aim the system primarily at commuters...visitors will get a map and figure it out quite easily the way we do when we go to London etc.