This paper discusses about the original concept of Korean punctuation marks and the criteria to determine which is punctuation mark or not. For this purpose we did a comparative study of preceding research. We discussed that the preceding studies were a little fragmented, so they had insufficient definitions of Korean punctuation marks. Here, we suggest a new definition of Korean punctuation marks; that is, "Korean punctuation marks are regularly associated with modern Korean written language and they are accessory marks which add extra meaning into the sentence and help readers to understand. Next, we suggest five criteria which we may use to identify punctuation marks. First, historical criteria, punctuation marks are formed through diachronic streams. Second, ontogenic criteria, punctuation marks were originated not modern media, e.g. computers, cell-phones, etc, but traditional systems, e.g. books, newspapers, magazine, etc. Third, formal criteria, punctuation marks have only single-form. That means emoticons, which have multi-form, are not punctuation marks. Forth, non-iconicity criteria, punctuation marks have no correlation between their shape and functional meaning. Fifth, meaning criteria, punctuation marks have only functional meanings, not lexical meanings, and sometimes they partially express the aspectual meanings of speakers.