Excel Sparklines are a great way to visualize lots of data quickly. Differentiating the High and Low points within the Excel Sparkline pinpoints your strong and weak data points.
To enter a High or Low marker you need to click inside your Sparkline which will activate the Sparkline Tools Design tab.
You need to choose Marker Color > High/Low Point and then select the color that you want to represent.
Try it out by downloading the Excel workbook below.