Hello, new to this. Found a 1988 mint mark "D" and a "O" next to it so it looks like the word "DO".... I looked at it and I don't believe it is damage. What say you coin experts and thank you in advance.
Welcome to CT It hard to say From your pic when I enlarge it to blurry but it appears that it is zinc rot. IMO Dave
1988 Cents are Copper Plated Zinc They have many types of plating issues. Could be a Plating Bubble.. Not a letter O