A bit of research:-

"
that's just like the Japanese stamp to say it meets whatever standards i think.

Like an E mark for example.

You'll see jasma on most imported cars with after market exhausts.

Our HKS, Blitz, Fujitsubo Giken and Kakimoto exhausts were all JASMA stamped"

Apparently

"Japanese Automotive Sports Muffler Association

(JASMA)"

The association was formed to keep the Japanese government from driving tuning companies out of business.

By coming together they were able to get government sanctioning for their exhaust products.

Meaning during the shaken

(Japanese inspection) the car won't be faulted for having an unauthorized part.

They also ensure production quality, train/certify exhaust personnel, and stop false claims in advertising.

Not all exhaust systems are JASMA stamped meaning they are usually circuit systems, however certain circuit systems are JASMA certified.
https://www-jasma-org.translate.goog/?_ ... x_tr_hl=en