This is one cool old Bell R-T helmet with a unique paint job. The Yellow and black appear to be part of a customization. The white around the perimeter and down the center was most likely the original color. The black striping is actually a decal of sorts and not paint. The color scheme and layout hearken the Yamaha YZ of that period and my explain why this particular helmet has extra snap heads have been added around the jaw area, perhaps for a face mask?
Sticker size 7 1/8 or 57cm in place as well as SHCA approval. Chin strap stamped BELL R-T 10-76.