The mark consists of [the greek letter 'mu' (i.e. µ which stands for Micro) followed by the letters 'C/OS' and an optional version in roman numeral (i.e. 'II', 'III', 'IV' etc.)
GREEK LETTER "MU" C OS MICRO C OS GREEK LETTER "MU" C OS 2 MICRO C OS 2 GREEK LETTER "MU" C OS 3 MICRO C OS 3