These codes could benefit from some sort of distinct prefix so that users, browsers and apps could identify it as an open location code and treat it as such apart from a random string. Other examples being things like @username or #hashtag.
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.