This is tomorrow here is Bosnia and Herzegovina.
What's it all about? Google it! I say that because I don't want to appear either ill-informed or insensitive and I know enough to know there are different opinions about the day.
Are such disagreements so surprising?
Let me avoid any deep issues and give my less-than-totally-serious answer. Things surprise me less and less but I think, in a way, this is surprising. In the UK people don't seem to care what a Bank Holiday is for, just that it's a day off work. For example, I'm sure it's that inherent laziness, rather than deep-seated English pride, that fuels the annual call for St George's Day to get added to the list national days off. Here, it seems, people are perhaps more principled.
Anyway I post this picture for the friend who was really excited when we saw this sign during a Sunday afternoon stroll through her town centre.