Could you explain what you mean when you say that X does not have good connations in Japan? Is it related to the use of the letter X in reference to p0rn? That is the case in English but it doesn't stop the letter X from having good connotations in other contexts.
*Edited to bypass an overzealous language filter*
O = Good/Right
X = NG/Wrong
School teachers use these marks for test papers!