The Maltese cross is a cross with four arms of equal length that expand outward and end in a "V" shape. The cross was originally the symbol of a group of 11th century knights, known as the Order of Knights Hospitaller (later the Knights of St. John), who cared for the sick in a Jerusalem hospital. Firefighters around the world now wear the Maltese cross as a symbol of honor and courage.
Public Domain is a copyright term that is often used when talking about copyright for creative works. Under U.S. copyright law, individual items that are in the public domain are items that are no longer protected by copyright law. This means that you do not need to request permission to re-use, re-publish or even change a copy of the item. Items enter the public domain under U.S. copyright law for a number of reasons: the original copyright may have expired; the item was created by the U.S. Federal Government or other governmental entity that views the things it creates as in the public domain; the work was never protected by copyright for some other reason related to how it was produced (for example, it was a speech that wasn't written down or recorded); or the work doesn't have enough originality to make it eligible for copyright protection.