Building on the last post from Aluminumfoil: also a tag for overgrown. Walls could be described as ivy covered after a certain period, or field and yard’s being “overgrown”, or turned to shrubs. And what about moldy buildings?
Decay over time is something I want to do, but that’s further off still 
Basically each tile type would need to have a half-life and a decay product. Any time the map is loaded, it caclculates a probability for each tile, and if it fires, changes the tile to the new thing (moldy wall instead of wall, or vine covered, or crumbling).
The same thing could apply everywhere, weeds growing through asphalt and concrete, underbrush growing thicker, even buildings collapsing.
Decay/change over time would be amazing and truly, truly unique in the entirety of gaming (especially if it went from as it is now to a sort of mad max/fallout esque world after a couple of years, however I do agree that just some ‘crumbling wall’ tiles/rubble/broken windows would be a good substitute for now.