Japan High Speed Agency Industry, Tokyo, 1953-60
The Japan High Speed Agency was set up in 1953 by Yamada Ring Sengokan (山田輪盛館) which was in business from 1909 through till 1968 (per the Japanese Wikipedia). The parent company was an importer of vehicles and motorcycles. The subsidiary, Japan High Speed Agency, made the HOSK (ホスク号) brand of motorcycles which included both 2 stroke (123cc) and 4 stroke machines in displacements ranging from 248 through to 500cc. The 500cc twin released in 1955 is interesting as it was supposedly a refined copy of the 1951 Horex 500cc twin called the 'Imperator'. The production rights to the HOSK were sold to Showa in 1960 and then again the same year to Yamaha who went on to develop the XS650 from the HOSK design.
HOSK is an acronym based on the first initials of the design team (Hori, Ozeki, Shimizu and Kimura).