it's ะ with final consonant --> ก + ะ + น you will get กัน (gun)

It indicates the syllable is short! It's also written as " ะ " at the end of a word - it's tucked on top of the syllable if it's not the final syllable. The opposite is " า " (not the "ว/w" character; that has a loop), meaning the syllable is long.