After about 1918 they changed to "...CT. U.S.A." and as often as not Special is abreviated SPEC.

On page 275 of The Parker Story they show the rib marking on GHE serial number 237134 -- "PARKER BROS. MAKERS. MERIDEN. CT. U.S.A. PARKER SPEC. STEEL"

On page 276 they show the rib marking for GH-Grade serial number 174013 -- "PARKER BROTHERS MAKERS,MERIDEN,CONN.PARKER SPECIAL STEEL"