I've seen Hercules bikes with just an "H" in the chainring. The one I pictured has never been dated nor has the model been seen except this one time. Best guess is sometime in the '40s or early '50s at the earliest. I found it in my town dump and have since passed it along to wahoonc. Possibly this decal will help you ID the bike you are looking at. Maybe wahoonc could provide a pic of the headbadge.