Religious symbolism in murals is common across cultures and time. Early Egyptian murals, for example, depict the gods Rah and Osiris and the goddess Isis. More subtly, a work that draws from Christianity might contain a serpent, an apple or other symbol of Christian beliefs. Among many Hindu symbols, saffron gold represents purity and blue represents infinity, thus the god Vishnu often has a blue complexion, symbolizing his infinite nature.
Symbols from classic mythology are very common in paintings of all kinds, including murals. Michaelangelo even used them in the Sistine Chapel. In his painting of the last judgment, he included Charon and his chariot, with Charon representing the passage to Hades that the damned will face. In a long list of mythological symbols, the phoenix, a bird who rises from the ashes, symbolizes rebirth. The cornucopia, or horn of plenty, represents Demeter, goddess of the harvest, and thus abundance, and the lyre, the instrument of Apollo, god of music and poetry, often represents the arts.
Murals with political symbols often depict territories, iconic events, heroes and leaders. When a flag appears in a mural, it nearly always symbolizes a country or revolution. In murals that were painted in communist countries or by artists such as Diego Rivera who had communist leanings, it is not unusual to see depictions of peasants, who are symbols of the strength and dignity of the people. In Egyptian murals, the lotus was an Egyptian symbol representing Upper Egypt. Papyrus symbolized Lower Egypt.
Some items and images in ancient murals appear to be symbolic, but scholars don't know for sure what they symbolize or whether they are symbolic at all. In the prehistoric murals in the caves at Lascaux in France, a small bird on a stick sits next to an image of a man who has died or is wounded. No one knows for sure what it represents. A fresco in ancient Pompeii depicts an orb on a table with columns on either side and what appears to be laurel branches suspended behind it, but no one knows if the orb is ceremonial or whether it's just a decorative piece.
Many murals depict daily life, but even these murals often contain symbols. You may find a crest symbolizing a family. Images of people harvesting are a symbol of abundance. In some contemporary murals, you can find sports symbols. For example, if you go to a fast food restaurant in a town that hosts a Big Ten school, you will likely find a mural containing the university's team mascot and colors, both symbolic of the school. Ancient murals in Pompeii and Herculaneum that survived the explosion of Mount Vesuvius depict daily life, including fertility symbols, and to ward off the evil eye, phallic symbols.