I don't know about sports clothing (tennis, running, etc.) but, for outdoor gear, there are absolutely boutique manufacturers of jackets and so forth (e.g. Feathered Friends in Seattle). Don't know of the top of my head if they have visible branding or not. Logos aren't universal though. I'm looking at a Merino wool LL Bean zip-neck shirt that doesn't have any external logo or branding on it.