Drawing on mouse location

Question

Guys i'm trying to print text over the top of a background graphic where the mouse is clicked on a click event, so for instance if the radio button is true where ever the mouse is clicked it will print "DL" on the screen.

Something like:

if (radioButton_DL == true)
{
  Print "DL" at mouse coordinates on screen.
}

What would be the best way to achieve this?