Those net safety vests that have a reflective stripe work well IMO for road construction crews. Perhaps they'll work great for those you wish to help.

However nothing is a guaranty all the time. There'll always be some situation where a particular safety thing isn't the best choice. And there is no guaranty that all the homeless and other's on bicycles will be perceive your kindness for what it is. A lot of homeless already have mental issues from PTSD or actual brain injury from concussions and other things. So make sure you are careful.

If you haven't had, then maybe getting some information from food kitchens and other services for those types will help you in dealing with their peculiarities.