That bar means that the preceding syllable 'ka' is elongated. As the Japanese sound system doesn't enable its speakers to produce the 'r' sound alone, they elongate the vowel immediately preceding the 'r' as a kind of a make-up for the absence of the 'r'.
Incidentally, there is a top-selling snack named カール in Japan, so people won't have a hard time remembering your name there.