[gurkendoktor]

Reminds me of how I use [x] to tick boxes in paper forms in Europe, but I was told in Asia (Taiwan) that I should use a check-mark instead. x is no.

[_delirium]

I think check-for-yes, x-for-no is a fairly common convention in English as well, just not in tick-box forms. You do see it in feature-comparisons grids a lot, often with the check-mark colored green and the x colored red, to mix in another convention. Example: http://prezi.com/pricing/