[support] How can I tell if a user if a user is a member of an OG group?

I would like to show a link on a group node if a user is a member and another link if they are not. I looked through og.module and found the $subscription variable. I tried both the following without any success:

<?php if($subscription == 'active') : ?> already a member! <?php else: ?> Join Today! <?php endif; ?>

<?php if($subscription) : ?> already a member! <?php else: ?> Join Today! <?php endif; ?>

But I'm getting "Join Today" showing whether the user is a member or not. I imagine this means the $subscription variable isn't available in this context.

does anyone know how to find out if a user is a member of an OG group?

Neil