The ride sign up sheets are now available as customized versions in the ride schedule. Just click on My Rides and then on the Sign Up Sheet link for the ride you are interested in. You will then have a fully customized sign up sheet to call your very own! You can not print customized sign up sheets unless you are the leader, or coleader of the ride, or if the ride has already happened.
Or, if you are still old fashioned, you can print out the old sign up sheet here. Just a warning though, this form will probably not be updated in the future.