You can now signup for a NETRA membership completely online by going to http://netra.org/memberships/new. If you are an existing member, you can also renew your account without having to send in any paperwork. Just log into your account and click on "Renew Membership" in the sidebar and follow the steps.
Definitely signup for your account before the season gets underway so that you can avoid the long lines at the next event.