I personally feel that as the vast majority of people, either born in Wales, other parts of the UK & other countries speak English, that it makes far more sense for safety signage to be in the English language. Making them bilingual can be dangerous.
Place names, on the other hand, should keep the names used by the majority of those living close by. Street signage in new estates should as much as possible be in the Welsh language in Wales. No-one has a problem with Llangollen, Caergwrle, Cefnybedd, Coedpoeth or Gwersyllt etc so why would new villages & streets be bilingual?