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In the 2000 South Korean Revised Romanization, the "hyphen optionally disambiguates syllables" to indicate syllable boundaries. (Ref.) Although the Wiktionary convention, as of 2022, uses the apostrophe, eg 가을 (ga'eul instead of ga-eul).

For the McCune-Reischauer Korean romanization, I did not find references for a corresponding marking, although the apostrophe "is also used to separate n and g when they do not form the single sound". (Ref: p.3 of this PDF.) -- Note to self