The fu symbol actually consists of two distinct characters. The lines and squares on the right are indicative of fertility (variously representing grain, a farm or something similar), and the standing character on the left is a heavenly figure (Fu is also the name of a god) offering a blessing. Together, they represent good luck, probably via a bountiful harvest.

The word "fu" in Chinese is very similar to the word for "bat", hence bats are also symbols of good luck in Chinese culture.