We've shifted our office organization around, and now our group shares a floor with three other groups with whom we had not shared communal space before. In the prior setup, there were three larger central kitchens that the entire company shared (and at least one of them had a hot-water dispenser). Now, each floor has its own kitchen with fridge, microwave, etc. Two kettles for boiling water for tea/coffee have appeared in the kitchen, and I know they must belong to someone in the other groups. We don't cross paths very often, and even if we did, I'm not sure who I would ask about ownership.
So, the central question is: Can I use the kettles? Are they tacitly communal property since they're on the kitchen counter? Or should I put up a note asking if I/others can use them? If so, how should such a note be phrased?