The signs should be written according to the local name and pronunciation. The whole point of putting up a useful sign is to indicate the name as it is actually used. Support the established orthography rather than new inventions. As for the other languages, established orthography should be used. The Bible Society of the Presbyterian Church has a wealth of information on the orthography that's actually used on a daily basis.
Street signs demand good typography,including both legibility and aesthetics.
A couple of years ago, I noticed that about half of the street signs in Taipei County were vertical. Even the romanized names were typeset vertically in very small letters, rendering them hardly legible. An illegible sign is a useless sign, nothing more than a waste of taxpayers' money. Street signs in cities should follow these good examples. Street signs are a reflection of the overall language policy of Taiwan.