Yep this would be a 230.2E requirement if you are allowed to do it. (If it is two services!? You should check that "Special permission" before you build it...) And if it is allowed, still a bad idea, (from two services, especially if not located together.) its not like two different systems of different voltages. You would need the signage to let you know there were two sources... See 225.37
Although these would be two different systems, and need to be identified as such. That means Neutrals and Grounded conductors to identify "system" if in the same conduit, or boxes. Although they might be the same voltage, if they are on different transformers, they are different "systems".
A while back I did a resturaunt with 4 different transformers to 8 panels, all same voltage. It was easier to run all the circuits together. So I got rolls of all my colors... ABCN with black stripe, ABCN with red stripe, ABCN with blue stripe, and no stripes. (The black, red, and blue were slightly different than main color with contrasting boarder.)
My wife works at a disaster control center, and it has several services, and generators all right next to eachother. And a really interesting array of transfer switches. All can be switched to different loads. And it can shed non-critical, all the critical stuff is on UPS. If the door wasn't always locked, I'd get a picture... But it has a huge warning on the door, "Authorized personell only - This facility powered by multiple sources"
