Misago/misago/emberapp/app/templates/components/guest-nav.hbs

<button type="button" class="btn btn-default btn-login navbar-btn btn-sm" {{action "login"}}>
  {{gettext "Sign in"}}
</button>

<button type="button" class="btn btn-info btn-logout navbar-btn btn-sm" {{action "register"}}>
  {{gettext "Join now"}}
</button>