Similar to a cutie mark, a zebra's glyph mark is a representation of self. How they differ is in both appearance and purpose.
While a pony's cutie mark appears in youth, often alluded-to by their birthname and representing a particular talent or craft they intend to devote their lives to, a zebra's is more present or backward-focused, representing who they are as of now in a less specific sense and rarely, if ever, have any connection to their name. It also develops over time as who they are as a person changes throughout their lives. This is best illustrated by examples.
A zebra with an adventurous spirit might have a map that grows as the zebra visits more countries and charts the land, literally depicting their travels through the world. On the other hand, a scholar devoted to the study of flora might develop a flower or sun that slowly expands throughout their life, adding pedals or rays and other flourishes as they feed their passion.
For others, the mark might seem to adapt to the changes and stresses they face. A zebra devoted to the healing arts might begin with a heart or cross depicted on their flank. If drawn into a time of war that mark could become emblazoned with crossed swords to depict their new struggles. Then in her old age, as she retires to concentrate on the protection and healing of her own family, that mark may become surrounded by a shield, completing their glyph of a coat of arms to show the strength the zebra brings to her family.
But of course, there will always be zebra who do not grow, but become set in their ways, stubborn and shortsighted. More often than not, their glyph doesn't grow beyond the foal's scribble they first developed in their youth.
The size, scope and complexity of the mark depicts the depth of a zebra's wisdom, intelligence and skill. Their understanding of their life and that of those among them. Often, the zebra with the largest glyph is elected as the leader of a tribe or community and legends of the greatest zebra to have lived inevitably describe mares and stallions whose marks could cover their entire body.