That sounds like me, except I don't need to wear branded stuff much. Can you get away with wearing just a button or a pin? Or a cap or something else small? Or maybe just carrying a tote bag or briefcase with the brand name prominently on it? That would give you a lot more leeway with clothes.
We have some branded stuff too that I hate, but wearing it is optional. I try to look professional when we're out travelling, but luckily in my line of work professional equates rubber boots and goretex jackets ;)
Anyway. The hippest mom - and new grandmom - I know at work is also a cyclist, and wears lots of knee-length, colourful dresses. Not frilly feminine ones and not closefitting sexy ones, but semi-fitted, artsy detail, fun Pippi-like dresses without looking childish. A bit like some of these:
www.desigual.com. And colourful shoes and boots. She looks fantastic.