RIC gives four theories about the meaning of the bull of Julian as shown on this coin.

1. It could represent the Apis Bull, which lived in Memphis in Egypt. The Apis bull was a black animal with a diamond-shaped white mark on the forehead and several other distinctive marks and characteristics. It was revered,sometimes treated as an oracle, and was fed from golden bowls. If the holy animal died, it was embalmed and entombed with great ceremony. A state of mourning was then prescribed until a new Apis Bull could be found, so to minimise this, normally another sitable bull would be kept ready as a precaution. However, if the old bull reached the age of 25 years, it was in the temple lake and a new animal took its place without ceremony. In the year 362 A.D. a new Apis bull seems to have been found, and the coin might therefore allude to this.

2. It could be a favorite creature of Julian. I don't know whether it actually was a favourite of his.

3. It could be the astrological birth sign of Julian. Julian was possibly born in May in 331 CE (this is not definite) under the astrological sign of Taurus, the bull. In this theory, the two stars above the bull represent the two most important light areas in Taurus – actually, both are groups of stars: the Pleiades and the Hyades. The bull itself represents a combination of Taurus and Apis.

4. It could represent Julian himself, as guardian of his people. In ancient philosophical writing, for example Dio Chrysostom, the emperor has been compared with a bull that stands guard over its herd. In this theory, the legend on the reverse of the coin, SECURITAS REIPUB (the security of the state), suggests that this is how the bull is to be undestood. But this does not explain the two stars.