I've been fleshing out the unseen or unacknowledged ranks and rank insignia of Starfleet.
Most supplemental material refers to O'Brien's single black pip as being the designated rank for a Chief Petty Officer. However, I have the sneaking suspicion that it was actually supposed to be a Warrant Officer's insignia. Proof is that concept art for VOY shows a single black stripe as the Chief Warrant Officer's insignia, not the CPO's.
The writers played very fast and loose with O'Brien's rank, and even in the TNG episode where he's established as CPO he still wears lieutenant's pips. In TNG he eventually starts wearing a single black pip like a few other one-off characters, but because his rank was so all over the place back then I'm willing to accept this was still a costuming error. It's not until DS9 that they really settled on his rank and gave him a unique dedicated insignia.
The clincher for my theory is that, allegedly, early script notes for DS9 (while O'Brien was still wore the black pip) call O'Brien a Warrant Officer. This piece of trivia is upheld across several wikis and fan-forums. However I can't find any basis whatsoever for this claim.
Does anyone have proof these notes exist?