My stock TE511 muffler is stamped... USDA approved spark arrestor. Unless it is eatable I would say it is supposed to be stamped USFS. Funny stuff. I did notice this last ride (friends trying anything they can to keep up with the mighty 511 ) so maybe there is a need for USDA approval.
It is not a typo. Since 1905 the Forest Service has been a branch of the USDA. USDA Forest Service San Dimas Technology and Development Center 444 East Bonita Ave. San Dimas, CA 91773