The easiest way to communicate with another trader on the other side of a noisy trading floor is to use hand signals.

Ryan Carlson, who has worked at the Chicago Board of Trade, the Chicago Mercantile Exchange, and the New York Mercantile Exchange, is responsible for TradingPitHistory.com. The site is an incredible database of hand signals that traders have used to communicate across trading floors all over the world.

We recently got our hands on a copy of "Trading Pit Hand Signals," and we were particularly fascinated by the hand signals used to indicate the various brokerage houses.

"The ability to recognize all market participants was what made open outcry trading transparent and from this, signals were developed for the larger brokerages and for some large local traders," writes Carlson on his site. "In cases where a more universal signal was never developed, their hand signal in the pit would simply be their three digit firm number."

Below are the hand signals used by CME traders to identify some of the big Wall Street firms (some of which are no longer with us). You're probably going to have a hard time forgetting them.

Thanks to Ryan Carlson for giving us permission to feature these images.