<% Membership.username %>
macro renders the username

Sourcecode in Membership/macros.js:
1:   function username_macro(param) {
2:      if (param.linkto && (param.linkto != "edit" || this.user != session.user))
3:         Html.link({href: this.href(param.linkto)}, this.username);
4:      else
5:         res.write(this.username);
6:      return;
7:   }