In
Unicode, the dotted circle (◌) is a non-significant typographic character used to illustrate the effect of a combining mark, such as a
diacritic mark.[1]
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):
Diacritic ̒ used alone between regular spaces
Diacritic ◌̒ used after a character
Using the generic dotted circle character also shows the relative positioning of the diacritic.
References
^"Chapter 17. About the Code Charts"(PDF). The Unicode Standard. Version 6.2. Unicode, Inc. 2012-09-26. p. 273. Retrieved 2015-03-28. Combining characters are shown with a dotted circle. […] the relative position of the dotted circle indicates an […] approximate location of the base character in relation to the combining mark. […]