I'm afraid you are taking a risk in hosting a ride as an individual. If something were to happen to one of the participants that rode because of an invitation from you (poster, verbal or otherwise) the primary target for the lawsuit will be you. I take this risk too everytime I call up a friend and ask them if they want to ride. What a shame that we have come to this. Best advice for you and me is try your best to pick a safe route and not take a busy route or route with narrow shoulders, obey all traffic laws and wear a helmet.