I've never heard of that before.
To be honest, I don't know what the "correct" way is. I do it with three fingers together and the ring finger and pinky tucked in. But a quick perusal of fisheaters.com revealed this:
The Sign of the Cross is made thus: First choose your style:
Option A. With your right hand, touch the thumb and ring finger together, and hold your index finger and middle finger together to signify the two natures of Christ. This is the most typical Western Catholic practice.
Option B. Hold your thumb and index finger of your right hand together to signify the two natures of Christ
Option C. Hold your thumb, index finger, middle finger of your right hand together (signifying the Trinity) while tucking the ring finger and pinky finger (signifying the two natures of Christ) toward your palm. This is the typically Eastern Catholic practice.
Option D: Hold your right hand open with all 5 fingers -- representing the 5 Wounds of Christ -- together and very slightly curved, and thumb slightly tucked into palm
touch the forehead as you say (or pray mentally) "In nomine Patris" ("In the name of the Father")
touch the breastbone or top of the belly as you say "et Filii" ("and of the Son")
touch the left shoulder, then right shoulder, as you say "et Spiritus Sancti" ("and of the Holy Ghost"). Note that some people end the Sign by crossing the thumb over the index finger to make a cross, and then kissing the thumb as a way of "kissing the Cross."