It all depends on the country where you report it. Germany is at least in my experience serious about it.
I would recommend something like peeblebee, but modified in a way that It recharges from the bike generator. Depending what kind of front lamp you've got, it might be possible to hide in there with some tinkering.
In a project I'm in there are 20 commits just labeled
.. The only reason I haven't slapped them silly is they left before I started.