Here's a great depiction of the pigeon drop scam, from the 1967 movie The Flim-Flam Man. This scene stars George C. Scott as the con-artist and Michael Sarrazin as his apprentice. Slim Pickens plays the victim - the pigeon - who gets conned.
The movie wants you to identify with anti-hero Mordecai Jones, played by Mr. Scott, so it makes Slim Pickens's character look like a greedy bastard who gets his comeuppance.
The pigeon drop scam is found in many variations. In its basic form it involves a large sum of money that you want a piece of. Others also want some of the money. These others convince you to put your own money into a pot that everyone will share. But all the money vanishes, and you're left with nothing.
To avoid getting ripped off, never give someone you've just met any of your money and expect that you'll get more money back. Those kind of street investments are always bad investments.
Take a look at another con game (now obsolete) from the same movie: The Punchboard Scam>>