There are two ways to denote chords in ABC. One is to use quoted chord names as Snuffy said. The other is to enclose the notes of a chord in square brackets. A D Major chord might look like [D,F,A,]. In the key of D Major the F, is taken to mean F# below middle C. Using bracket notation, the chord is set as notes in the score instead of chord names above the score.

An excellent reference and tutorial on ABC coding may be read or downloaded from The ABC Plus Project page.

      - Mark