Around 2009/10 I remember a particular style of bag being pretty popular amongst fixed gear riders. It was a black backpack with a roll top/flap top and white branding/logo on it, I'm pretty sure the material was similar to the shiny cordura that Chrome makes their messenger bags out of. The manufacturer might have been Japanese, and I'm pretty sure the Mash SF guys used these bags in some of their videos.

Does anyone know what I'm talking about?

SAGlife or Mission Workshop most likely.

I’ll second Mission Workshop. San Fran’ based. Started in ‘09, one of the co-founders, founded Chrome industries.

I always say get a bag that works for you. Don't worry about the trends or who is wearing what make sure that bag will do what you need it to do and is comfortable and fits you well.

Pretty sure you're thinking of T-Level bags, kind of hard to find here. Mostly an Asian brand I think unless you can find a site that imports them.

Yesss SAGlife was the one, thank you