Currently there are only three properties exposed by the MarkersAppearance - MarkersType, BackgroundColor and Visible in AreaSeries, LineSeries, ScatterSeries and ScatterLineSeries. Expose more properties like Size, BorderColor and BorderWidth for the markers in the mentioned Series. For the time being the following workaround can be used:

        function pageLoad() {
            var circle = document.getElementsByTagName("circle");
            for (var i = 0; i < circle.length; i++) {
                //Modify the size of the marker
                circle[i].r.baseVal.value = 15;
            }
            //Modify the width of the marker border
            $telerik.$('circle').attr('stroke-width', 13);
        }