I was unaware that there was such a thing. I know what atheists are but had no idea that have formed an international movement. I am unsure, personally, but am open minded enough to say it really doesn't bother me if one is a believer in a god or not.
I just get a blank page when clicking the link. I tried Googling but don't get a whole lot, mainly articles about "open secular" itself, which seems to be a coalition of groups headed by Richard Dawkins (I have no idea who he is either and didn't look him up). It doesn't seem to be "international" but these articles are from last year; maybe they gained some more groups overseas. It also just seems to be a "self proclaimed day".