195 is not in the ASCII range. Unfortunately there are many sites around which show "ASCII tables" containing characters over 127. These are often called "extended ASCII" - often with a false implication that there's only one such encoding. .NET uses Unicode - and each char
is a UTF-16 code unit. So (char) 195
is actually U+00C3, which is a "Latin capital A with a tilde".
The character you were looking at wasn't even a tick - it was a square root sign.
For an actual tick, I suggest you want U+2713, which you'd add like this:
item.SubItems.Add = "\u2713";
Of course, that relies on the font you're using supporting that character.