We use the same letter that is used to name the musical notes as chord symbols:
A letter by itself means a major chord:
For minor chords we add m (lower case), min or the symbol -:
Add dim or the symbol o :
Add aug or #5 or +
As with triads, to indicate an inversion, we add a slash and specify the note to be played in the bass:
See also: Seventh Chord, Ninth Chords, Other Extensions