Event.onDOMReady(function() {
    $('pn-login').down("a").observe('mousedown', function(evt) {
        var properties = {
            eVar1: AC.Tracking.pageName() + " - login click", 
            events: 'event20'
        };
        AC.Tracking.trackClick(properties, this, 'o', 'Login Click');
    });
});