"Silver hallmarks in the UK date back to the medieval period and the practice of applying them as a guarantee of the purity of the precious metal represents Britain’s oldest form of consumer protection."

https://www.antiquestradegazette.com/guides/information-guid...

The romans would have had guild marks on things like pottery, I just don't know of any online guides for them.

You didn't have mass distribution on the scale you have today without middlemen, and so word-of-mouth and personal recommendations should have probably sufficed for most markets, as they do in some markets today (e.g. job and employment)

In all probability, people's names were their own brands, like they still are in small towns today.

I can imagine two Romans walking down the street, and one saying to the other "Oh our family has been buying meat from Spartacus' family for generations now, they're the best when it comes to that sort of stuff."

Or place's names, like Champagne.

I don't know about commercial brands but some gladiators were paid quite handsomely by sponsors[1], not unlike top-tier athletes today (actually, some arguably earned more than modern athletes[2])

[1] https://www.forbes.com/sites/drsarahbond/2016/08/10/how-athl...

[2] https://www.thevintagenews.com/2017/01/18/the-highest-paid-a...

Falernian wine would probably count as a "brand" of wine.

https://en.wikipedia.org/wiki/Falernian_wine

The baker down the street was the only "brand" of bread available, I suspect. Although personally knowing who is making the product fulfills a similar function to branding.