>>373174304
Late reply for you anon:

>so it's got to be possible for a VRC world to grab data from avatars.

The 9/11 event used shaders, so it could be put on anything. An easier way to recognize just your own avatar is to use vrchat API's GetBonePosition() in udon to get the transforms of a mechanim bone in your avatar's rig. Then measure a value you think will be unique to that avatar like the angle between the head and eye bones or distance between head and neck etc. Jaw bone is typically unused and might be useful too.