The symbol -||- was mentioned in the document “Best practices for prompt engineering with OpenAI API” on the OpenAI Help Center (Best practices for prompt engineering with OpenAI API | OpenAI Help Center).
It appears that the symbol represents “Same as above format,” which in this document refers to a comma-separated list of company names. I am curious as to why this symbol was used.
What you’re referring to is called “ditto marks”, OpenAI uses the Scandinavian format, probably because many other types of ditto marks will break your json formatting
You can read more about it on the wiki: