Penny is made from copper, which is one of the oldest metals used by humans. It has played an important role in mythology. Its primary use has been as a specified metal in rituals, but it has also represented the Greek God Venus and to the Greeks, it could protect against evil and attract love. Find a lucky penny means you are being protected against any evil energy, and you can use it as a lucky charm.
The reason why finding a penny on heads up brings good luck ranges from early beliefs about where metal came from to the notion that money symbolizes power. The notion that only a heads-up penny brings good luck comes from a doctrine that that a face-down penny is not of a neutral character. It is said to be unlucky and should be avoided. For more details, visit http://www.pennypriestess.org/pennymysteries.htm.