You can use as a reference, any regulation or recommendation, such as ANSI / IEEE Std 91-1984, but more important is to maintain consistency across all documents.
Use a standard, has the advantage that when you refer to it in your documents, there is no possibility of ambiguity.
You can also write an internal document to your organization (such as a long time ago) where you specify the documentation system chosen. If the documentation gets to outsiders, you can always attach a copy of the internal standard. This has the advantage that it can write the internal document agreeing between all stakeholders.
For this particular question, the standard referred to above, implements only dot without adding the bar on the label.