I think it'd have to be a DOT approved helmet, but considering the plastic beanies the harley guys are tending to wear these days, apparently the DOT certification is not that stringent.Depends. If it has a motorcycle plate, or is missing a front plate in a 2-plate state, that is going to be a dead giveaway. If I got a coin strap for my hard hat, do you think that would count as a helmet?