I've always been one to not like drawing attention to myself. I mostly train on a college campus and a city playground. Our local group usually practices together on weekends, so the campus is not very active, but the playground is filled with people during warmer weather. If people see me training, so be it, but I don't go out of my way to be noticed. We've had younger teens approach us at the playground on several occasions and ask us what we are doing, so we explain and show them a bit about what we do. Some have heard of Parkour, most have not. The attention we have gotten though has been positive.
Though I train in public, what I do is for my own benefit and to help others, not to be "noticed". It is keeping ourselves physically and mentally fit, it is for building community, and it is for having fun as well.