Working/idle animation on barracks, provision house and book binder (possibly other buildings aswell?).
So you can see if they are working or idle without clicking on the building.
Could be as simple as smoke from the chimney when the building is working/producing.
Thanks,
Jesper
or a mail in the mailbox when they go idle.
This is a great idea, MrsFlurry.
The barracks already has an animation. The animation could just stop when the barracks is idle.
Book-binder already has an icon over it when it's finished making a book, and I believe most players collect the book and immediately start a new one, making the 'completed book' icon the same as idle anyways. This week's maintenance will add a similar thing to the Mayor's House for collectibles.
The Prov House (and Rarity Prov House), on the other hand, has no animation. Both of them have a chimney though, so your 'smoke' idea would work, and the smoke animation already exists for other buildings, so should be easy to add here.