Can anyone suggest a good macro to allow me to select (touch) any cell in
a given range, and have the alpha character "X" (capitalized) appear in
the cell when the cell is selected?

For example, let's consider cell A1. A1 is initially blank and void of
any formulas. If I select A1 with my mouse, I want "X" to appear in A1.
If I select A1 again, I want X to disappear from A1, and so forth and so
on.

(Note: For my purposes, I prefer not to use a checkbox or radio buttons
because I already have conditional formatting depending on the contents of
the cells which will either have X or not.)

Thanks much!

Joseph