Sertum 500

Sertum was an Italian manufacturer in business for only twenty years, from 1932 till 1952. Within a couple of years of production they were producing a full line of 175s, 250s and this bike; the 500 sidevalve twin. The bear on a spring in the ad refers to the patented suspension system.
 By the early 1950's their product line was obsolete, they had not anticipated the exploding moped and scooter market and ceased operations in 1952.