Nothing quite draws attention like putting two fingers in your mouth and letting out a piercing whistle. Sometimes called the "cab whistle" because people commonly employ this technique to hail city taxis, whistling with two fingers produces a higher sound than simply whistling alone. The process is sometimes difficult, but with practice, you too can learn to whistle with two fingers.
Hold your thumb and index finger about 1/8 inch apart, almost as if you are forming the "A-OK" sign. Place the fingers just inside your mouth, enough to close your lips over your fingers. Keep the gap to allow air flow between your fingers.
Push your tongue back behind your bottom row of teeth. Allow the tips your fingers to rest against your lower teeth.
Press your lips firmly against your two fingers. They shouldn't be loose but rather stretched across your fingers. Flatten your tongue.
Inhale deeply, then blow air into the "V" formed by your two fingers. Use your tongue to guide the air in that direction. Blow slightly downward until you hear a whistle.
Adjust your fingers, lips and tongue as necessary to produce a whistle. Blow harder to increase the sound of the whistle. You're now ready to hail a cab in any city in the U.S.