Joshua's mention of the bread symbol was new to me. Thanks, Joshua!
That specific design then must have been based on the panis quadratus:
Baking Bread with the Romans: Part II – Panis Quadratus
Taste the daily life of Romans with this recipe for Panis Quadratus: The infamous sectioned bread excavated at Pompeii and preserved for millenia after the…
tavolamediterranea.com