Alphabet in marker for chart lines

[mario]

How can I insert a alphabet as marker in the chart lines.

If I right click on a chart line (line chart), then patterns, markers, then
is there a way I can insert a alphabet or special symbols like "a", "c",
"delta(greek symbol)" etc.,

Please help

 

[Jon Peltier]

You could add a data label for the data point, edit the label (the default
choices would probably not suit you), and select the Center label position.

- Jon