I read a very interesting story about bread. It involved Romans and how they branded bread. it is said that ancient bakers used metal stamps. The stamps were used to identify the baker.
it is said that Most bread in Rome would be baked in community ovens so to be able to identify the bread customised stamps or brands like metal brands would be used. This would generally distinguish between bread made by families and bread made by bakeries.
The bread was a part of the a much bigger business, similar to big tobacco or big food, it would be fun and interesting to know if it was called big bread or magna panem in Latin.. It is said it was so big that it was regulated under the law as a commodity. It was regulated to the extent of weight, size and cost of a loaf. Selling underweight loaves got you a penalty, I don't think the penalty went to the extent of the circus or death.
So how the brands worked? it is believed that these brands would be left on top a loaf of bread while it cooked in the oven. So when the bread was cooked the bakers brand would be on the loaf.
So, how did they figure this out. Among the ruins of Pompeii, a lot of artefacts were found, including a perfectly preserved loaf of bread. On that loaf of bread was an inscription - celer, slave of quintus granius verus. This carbonised bread is actually quite famous.