The Old Masters were artists from the 16th, 17th, and the beginning of the 18th century. These artists used symbols in many of their works. The symbols used to paint or draw allegory in art were derived from ancient literature, mythology, and the Bible. This method worked well because educated people could read these works and be familiar with the symbols and people that couldn't read had heard the Bible stories.
Depictions of Saint Jerome picture him with a lion, bible or a skull. There is a legend telling the story of St. Jerome removing a thorn from a lion's paw and the lion befriended him. The woodcut St. Jerome in His Cell by Albrecht Durer (1471-1528 ) is an example of allegory art.
The Dutch artist Lucas Van Leyden (1489-1533), in his engraving Portrait of a Young Man with a Skull (1519), the artist has the figure pointing to the skull he holds. It is a warning to consider your conscience and mortality. These types of images were called vanitas.
The Venetian painter Giovanni Bellini (c. 1430-1516) was a Renaissance narrative painter and the teacher of Giorgione and Titian. His depiction of St. Margaret devoured by a dragon is representative of the Christian art symbol of sin and sinfulness ie; the sinful nature. The devil is called the devourer in the Bible.
There are many more works of art by the Old Masters that use Christian symbols that portray allegory in painting and other art mediums. These are some other Christian symbols: the crown, rose, lamb, dove, and falcon.
Pictures of St. Joan of Arc seen as a maiden with armor, sword, and a banner astride a horse is allegory art that is probably more recognized by people today. The War Savings Stamp Program of World War I and WWII aided in funding these wars. Boy Scouts and Girl Scouts sold these stamps. One of the posters of this program for WWI was Joan of Arc Saved France by Haskell Coffin (1878-1941). The slogan ask America's women to buy the war stamp to support the war.