Unclear if you already know this, but the usage of the plus sign and the name "plus codes" for this scheme serve exactly that purpose. If you see a code with a plus in it, with usually 2 characters after the plus, it is most likely a plus code. Speaking from experience it is relateively easy to quickly identify by glancing at a webpage or a body of text.

Additionally the plus serves a similar purpose to a dot in the decimal number notation: the plus is always put after the 8th character in the globally-adressed code. So if you see a code with plus after the 4th character, it is immediately clear that the code is a local-notation, and you need to know approximately what country or city this code is referencing to, in order to properly identify a point on the globe. Usually the locale is pretty clear and 4-6 digit codes are just fine, and the plus character provides a possibility to distinguish them from each other.