Fixed it - put this in the function showaddress(address) else that outputs the marker.

echo "icon = new GIcon(G_DEFAULT_ICON, "http://mysite.com/images/icon12.png");n";
echo "icon.image = "http://mysite.com/images/icon12.png";n";
echo "icon.shadow = "http://mysite.com/images/icon12s.png";n";
echo "icon.iconSize = new GSize(36, 22);n";
echo "icon.shadowSize = new GSize(36, 22);n";
echo "icon.iconAnchor = new GPoint(0, 22);n";
echo "icon.infoWindowAnchor = new GPoint(11, 1);n";