In general, coins incorporate various technologies to prevent counterfeiting.
One such anti-counterfeiting technique is micro-letters.
Note the “left hand” portion on which the myaku-myaku is depicted. The letters “オ,” “オ,” “サ,” and “カ” are inscribed in small katakana characters in four places on the left hand side.
They are not visible to the naked eye.
OSAKA＝オオサカ
It may be difficult to find coins with clearly visible letters.
