Baseball Sign Language
It's estimated that during a nine inning game about 1000 signals pass between catcher and pitcher, coach and batter, fielder and fielder and anywhere in between. A few are obvious, but many are clandestine touches, twists and even mimicry which an outsider has difficulties even noticing, let alone understanding.
Although it appears that there are several signs which are common to all games, the idiosyncrasy of baseball sign language is that it's highly flexible. The majority of signs are devised and agreed upon for each individual game in advance. They are different from coach to coach and may even be changed during the match. The catcher, who directs the defense from his position behind home plate, is a crucial figure in sign language communication. Signs direct the game and play a major role in winning or losing the match.
Here are a few basic signs and signals from catcher to pitcher:
1 finger up for fastball
2 fingers up for a curve
3 fingers up for a change up
Fist slammed on palm for a squeeze bunt
The catcher will also -through subtle hand and body movements -indicate the pitch location, for example high and outside and signal his set up.
These examples are just scratching the surface. There is an interesting video to watch. Manager Bill Masse of New Hampshire Fisher Cats explains some signs. Look at it at: www.youtube.com/watch?v=bLBT7H2P8vE. The video lasts only 1 min 47 sec and shows a few signals, but it makes clear how fast these signs are passed and gives a good first impression.
Another source of information on the subject is the book "The Hidden Language of Baseball" by Paul Dickson, published at Walker Books.