some of the forks had a stamped logo in the angled (bologna) cut on the bottom of the legs, these were the later forks! 83 or 84 onwards (not 100% sure on exact time these were released) this was done to identify genuine forks over the many copys being made
also genuine ones will have just 3 holes in the dropouts, bigger near the axle slot/hole & getting smalleer as the dropout tapers into the fork leg. often the copys had an extra hole for a wheel retaining tab!
welding wise they should be welded all the way up the outside of the dropout but have 3 welds on the inside edge, Top Bottom & middle for about a centimetre each
threadless will be stamped & much later
generally people want unstamped
i'll see if i can find some pics