That is a 1987 year mark I believe to have been stamped on a leftover blade remaining from the 4 dot run from 1981-1985. If that is so, the blade would not have been heat treated until after the year mark symbol was stamped. Perhaps when Joe returns, he can add to this. Paul Bos may remember also and he sometimes posts on this forum.
I am sorry I cannot be more definite in answering your question. By the way, is the blade mirror polished? I suspect it might be a gold etched blade because I have seen more gold etch blades than standard satin finished blades with this stamping.