Before revision: The non-obligatory symbol used in a mask work protection notice is Ⓜ (M enclosed in a circle; Unicode code point U+24C2 or HTML numeric character entity &#9410;) or *M*.
After revision: /U+1F1ADThe non-obligatory symbol used in a mask work protection notice is Ⓜ (M enclosed in a circle; Unicode code point U+24C2 or HTML numeric character entity &#9410;) or *M*.