I think that the #adhd symbol is fairly new but the symbol for #asd/#autism had changed from a puzzle piece (which autistic people themselves hated because it was most associated with #autismspeaks which is a company who thinks they can "cure" autism and other neurodiversities, so o guess we took it upon ourselves to find our own symbol
@realcaseyrollins and for the #adhd symbol they apparently actually asked #ADHD/#ADD people