I think you are asking about the heraldry of the shield. But for starters, the banner above the shield bears the University motto:
Leges Sine Moribus Vanae, translating to “Laws without morals are useless.”

The heraldry of the shield, in a nutshell, is that it combines the devices of the Penn family and the Franklin family with the colors of the national flag. The University is, of course, of Pennsylvania, and Benjamin Franklin played a large role in its founding.

Here are the details from the US heraldic register site:
"The arms of the University of Pennsylvania, also approved in 1932 and adopted in 1933, may be regarded as a symbol of the University serving a decorative rather than a legal function. The arms memorialize two important influences in the founding of the University, Benjamin Franklin and the Penn family. The heraldic description is as follows: "In the chief, gules, two open books and a dolphin, argent; in the ground, argent, a chevron, azure, with three plates, argent."

This design includes the three plates of the Penn family arms and the dolphin of the Franklin shield. The open books denote an institution of learning. The colors of red (gules) and blue (azure) are believed to have been chosen originally by a student representing the University in a track meet held at Saratoga, New York, in 1874. These colors were adopted by the Athletic Association in 1876 for use by University teams and by the Trustees in 1895 for use on the academic hood worn by graduates of the University. When the Trustees in 1910 adopted a design for the University flag they specified that: "The colors shall conform to the present standards used by the United States Government in its flags." The Red and Blue of Pennsylvania are therefore officially the hues maintained in the national ensign."