The utility knows, nobody else may know. For various reasons, now lost in the mists of antiquity, we have distribution at both 11kV and 13.2kV. The only way I can tell them apart is to look at a map, nothing in the field gives it away. Gotta be real careful in the places where both are on the same pole. That's only a couple of kV difference; for a more extreme example we have both 57.5kV and 115kV sub-transmission systems, but we quit buying 57kV insulators many, many years ago; anything installed since is suitable for 115kV so you could be looking at a stretch of 57kV and not be able to distinguish it from 115kV.
Then there's the utility where I used to live that started out life as a delta 12kV system and slowly converted to a wye 21kV system. The absence of a neutral meant 12kV, but you had to know that it really didn't have a neutral; I saw examples where a former 3 phase 12kV circuit became 2 phases and neutral of 21kV with the neutral on the phase insulator it had used back when it was a phase conductor. In that case, the real clue was whether the primary of the pole mounted transformers had two bushing "that" size or one bushing twice "that" size and one clamp.
Even the bushings might not help, as a Delta-to-Wye conversion like you describe likely re-used the transformers, now connected line-to-ground. Just because the H2 bushing is fully insulated does not prevent it from being connected to neutral, which may still be at the top of the pole since the neutral may have been a former "hot".
We have done it that way when we are doing a quick conversion.
THAT is why you need to consult the utility to be sure.
