The dotted circle, in Unicode U+25CC ◌ dotted circle (HTML ◌), is a typographic character used to illustrate the effect of a combining mark, such as a diacritic mark. In Windows, it is possible to use the key combination Alt+9676 to produce the character.
Illustration
A Unicode combining mark combines with a preceding character. When used as stand-alone, it would combine unintentionally with a preceding character (possibly a space):
Using the generic dotted circle character also shows the relative positioning of the diacritic.
References
Dotted circle Wikipedia(Text) CC BY-SA