Abdy is right, we managed to mount a decent resistance about a decade ago. We pushed all of the bears up to our polar regions (So, about 10km away).
The signs you see there are relics of how life used to be, and are also there to remind people that we always need new recruits for the Polar Guard.
The Polar Guard was formed to hold the line between civilization and the roaming polar bears. We've been able to keep them away for the most part, but recently there's been more and more breaks in our Guard. They just don't have the manpower, I fear the bears may take over again some day soon.