Anusvaara (or anusvaaram) appears in the alphabet of Indian languages like Sanskrit which use the Devanagari script, and in the Dravidian languages. Anusvaara nasalizes pronunciation of the vowel sound to which it is attached (namely, the one just preceding it). The exact nature of nasalization depends on the consonant sound which follows it (or if it is at the end of a word, by the "m" sound). In Sanskrit often the anusvaara is replaced by the corresponding nasal consonant.

In the Devanagari script, anusvaara is represented with a dot above the letter (मं). In transliterated form, it is written below the character (  ). Sometimes it is written above ( ṁ ). Both ways are correct.

See also 

Anunaasika