The person who quietly fixes the sign-up sheet before the event is leading, even if no one notices.

Leading is a set of actions rather than a position, and the actions often look like noticing a small thing nobody assigned and handling it. The sign-up sheet does not care whether you have a title. Groups run on a great deal of this invisible repair, and the people doing it are usually the reason anything works at all.

Find one thing this week that is broken, unowned and fixable in five minutes, then fix it without mentioning it. Do it again next week. That habit puts you in charge of things long before anyone votes.