your biggest obstacle would be finding the right paint/pen combination. i guess oil based paint markers would be your best bet for durability. they shouldn't wash off in the rain and will stick to most surfaces. problem is, they are also kind of notorious for running during use. you could end up with a bike with very drippy signatures. plus, there is a chance that names written early on in your trip would be faded by then of the trip.
interesting idea though. i'd do some tests before committing.