There are many ways to overcome this.
1. a. Put following in a cell and press Enter
c)
b. Go back to the cell and type first bracket to complete (c)
2. a. You can type (c) preceded with some special character and press enter.
b. Go back to that cell and delete that special character.
c. I have tried this with following special characters and found it working
!(c)
#(c)
!(c)
$(c)
%(c)
_(c)
\(c)
?(c)
2. a. Put only following entry in the cell
(c
b. CTRL+F
c. In Find What: box, put
(c
d. In Replace With: box, put
(c)
Note – The above will work with c) and replace with (c) also.
3. a. Write (c) in a cell and press space bar
b. Now (c) will get converted to copyright symbol. CTRL+Z
c. Now, (c) will be (c) only but it will have space after that.
d. If we don't want this additional character, we can replace this with space with blanks in CTRL+F window. In Find What: box, press space bar once (nothing in Replace With: box) and Replace.
4. For permanent correction – You can go to File > Options > Proofing > AutoCorrect Options > Locate (c) > Either delete this entry or put (c) in With:
Note – You can uncheck "Replace text as you type" to disable Replacing completely. But this would be applicable for all entries, hence not recommended.