The side of a penny that is good luck is the heads side of the penny.
Finding a penny with the heads side up is associated with bringing good luck your way.
And finding a penny with the tails side up is seen as bad luck possibly coming your way.
When you find a penny with the heads side up it's believed to bring you good fortune as well as good like.
And some people even will flip a penny over that they find tails up to make it heads up and hope to pass the good luck onto the next person who finds the penny with the heads side up.
The penny also is said to become good luck if you pick the penny up with your left hand but only works for found money on the ground that is loose on the ground that someone else lost.
However it's a superstition and does not always mean that you will have bad luck come your way or good luck come your way no matter which way you find the penny.
Still I always pick a penny up no matter if it's heads up or tails down.
It's not worth much but it is money.