An Anki deck I've downloaded is representing a word as "o-miyage" and "おーみやげ". The deck isn't using any kanji - it's based on JFBP book 1, which doesn't teach any kanji. I've hidden the romaji, so I'm only seeing "おーみやげ". I know the second character is intended to represent a hyphen, but it looks confusingly similar to the "ー" in "ラーメン".
Is there any notation used in the context of teaching of Japanese as a non-native language (or even outside that context!) to indicate prefixes such as bikago or suffixes such as "-や"?