Is it illegal to paint the curb?

I am going on a volunteer spree, and I was wondering if I would get arrested for vandalism if I were to take it upon myself to re-paint some essential city signage where I live? For example, there are some fading red-zones, handicapped zones/stripes, and loading zones that I would like to take upon myself to re-paint. There are also some fire-hydrants that could use a facelift. I live in Orange County, California if it matters at all.