All letters and symbols have a numerical code assigned to them in Windows and you can use these codes to type them. For example the code for µ is 181 and the code for ¢ is 162. You must hold the alt key down and type in the number code with a preceding 0, using the keypad (not the normal number keys).
So if you press alt-0181 you will get a µ micro symbol.
Excel has a function ‘CHAR’ used to display a character from a code, and a function ‘CODE’ to do the opposite and display a code from a character.
You could use “=CHAR(181)” in your formula.