Hand Signals for Chords

Want to play a song that's a non 12 Bar Blues on the bandstand in a jam situation?... use your fingers! As you're playing, hold the mic and harp with one hand and with the other use one finger for the I Chord... two fingers for the ii Chord... etc. If you place your hand behind your back the audience will never know. You'll of course need to be familiar with the chord changes (ask your guitarist buddy for those) and will want to practice this before hitting the bandstand (it can be hard at first to make signals and play at the same time).