I can't help but extend that metaphor - because they weren't even producing Ukrainian! Aieee!

"People are starving, no one has work, the entire structure of life is collapsing, but the first thing we do, let's kill all the hard signs!"

In defense of conquerors everywhere, I'd like to point out that fixing the strucutre of life (food, work, etc) is hard and takes a long time while changing billboards can be done relatively quickly and gives employment at least to the hardsign blotter-outers.
In other words, changing the billboards doesn't necessarily impede any of the post-conquest things that need to be done, it's just faster.

The absurdity of the situation here is that they kept switching the billboards when the conquest was not secure and they knew they'd probably lose the city, probably regain it and have to change them again.