Safety-wise, probably not, but the laughter might get to you after a while. Best not to wear black leather with it.

It will look somewhat unusual, and most motorcycle helmets are much heavier that bicycle helmets. But for security, it would be an advantage. 1) "What is the world coming to? A motorcycle helmet on a bicycle...?? How gauche!" Source and further information: http://news.motorbiker.org/blogs.nsf/dx/motorcycle-helmet-on-a-bicycle.htm 2) "It's not practical to wear a full-face motorcycle helmet on a bicycle any more than it is to wear a leather suit. Sure it is. What makes it not practical? The helmet isn't any heavier, larger, or less comfortable because you're on a bicycle. If you're going to be on a road without a protective cage, you should wear a helmet designed to actually save your life from the majority of head injuries." Source and further information: http://www.sportbikes.net/forums/3673807-post41.html 3) "I was just about to get a Brompton and an electric Brompton Nano kit, when I discovered that such a kit would turn my Brompton into a motorcycle. According to Belgian law, that is. Unfortunately, this would require me to wear a motorcycle helmet (ON A FRIGGIN' BROMPTON!? Can you imagine the sight of that? 15mph on a tiny foldy bike with a motorcycle helmet), get compulsory motorcycle insurance -- which doesn't come cheap! -- and it would have to be EU approved. Which I'm going to assume it isn't." Source and further information: http://forums.treehugger.com/viewtopic.php?f=1&t=3660&p=37171