Hi there,

The current request is kind of duplicate to the following feature request Show chart shapes in legend and regarding this I am going to decline it and move the votes to the other one to boost its priority in the backlog.

Regards,
Rumen
Progress Telerik

For the time being you can either use Visuals (http://demos.telerik.com/aspnet-ajax/htmlchart/examples/functionality/visual-templates/defaultcs.aspx) or use the following workaround in order to control the type, width, height and margin for the legend marker items:
		<script type="text/javascript">
			function pageLoad() {
				var kendoWidget = $find("<%=RadHtmlChart1.ClientID%>").get_kendoWidget();
				kendoWidget.options.series[0].legend = { marker: { type: "cross", width: 10, height: 15, margin: {top: 0} } };
				kendoWidget.options.series[1].legend = { marker: { type: "triangle", width: 15, height: 15, margin: { top: 10, bottom: 10 } } };
				kendoWidget.options.series[2].legend = { marker: { type: "circle", width: 10, height: 10, margin: { top: 0 } } };
				kendoWidget.options.series[3].legend = { marker: { type: "rect", width: 10, height: 10, margin: { top: 0 } } };
				kendoWidget.redraw();
			}
		</script>
		<telerik:RadHtmlChart runat="server" ID="RadHtmlChart1" Width="600px" Height="400px">
			<PlotArea>
				<Series>
					<telerik:ColumnSeries Name="Product 1">
						<SeriesItems>
							<telerik:CategorySeriesItem Y="15000" />
						</SeriesItems>
					</telerik:ColumnSeries>
					<telerik:ColumnSeries Name="Product 2">
						<SeriesItems>
							<telerik:CategorySeriesItem Y="45000" />
						</SeriesItems>
					</telerik:ColumnSeries>
					<telerik:ColumnSeries Name="Product 3">
						<SeriesItems>
							<telerik:CategorySeriesItem Y="5000" />
						</SeriesItems>
					</telerik:ColumnSeries>
					<telerik:ColumnSeries Name="Product 4">
						<SeriesItems>
							<telerik:CategorySeriesItem Y="5000" />
						</SeriesItems>
					</telerik:ColumnSeries>
				</Series>
				<XAxis>
					<Items>
						<telerik:AxisItem LabelText="1" />
					</Items>
				</XAxis>
			</PlotArea>
		</telerik:RadHtmlChart>
		<script type="text/javascript">
			dataviz = kendo.dataviz;
			deepExtend = kendo.deepExtend;
			ShapeElement = dataviz.ShapeElement;
			kendo.dataviz.LegendItem.fn.createMarker = function () {
				var item = this,
					options = item.options,
					markerColor = options.markerColor,
					markers = options.markers,
					markerType = "rect",
					markerWidth = 7,
					markerHeight = 7,
					markerMargin = { top: 0, left: 0, right: 0, bottom: 0 };

				if (options.series.legend) {
					if (options.series.legend.marker) {
						if (options.series.legend.marker.type) {
							markerType = options.series.legend.marker.type;
						}
						if (options.series.legend.marker.width) {
							markerWidth = options.series.legend.marker.width;
						}
						if (options.series.legend.marker.height) {
							markerHeight = options.series.legend.marker.height;
						}
						if (options.series.legend.marker.margin) {
							markerMargin = options.series.legend.marker.margin;
						}
					}
				}

				var markerOptions = deepExtend({}, markers, {
					background: markerColor,
					border: {
						color: markerColor
					},
					type: markerType,
					width: markerWidth,
					height: markerHeight,
					margin: markerMargin
				});

				item.container.append(new ShapeElement(markerOptions));
			}
		</script>