I'm taking the risk of making a fool of myself: this is simply something I've never seen before, to the point that I'm fearing a BFVFS.
I've switched to a medieval neighborhood I hadn't played in a while (different EA Games folder than the one I used up until yesterday). This lot used to be a cemetary, but I don't know if the tombstones are still linked to their ghosts (I don't dare load the lot yet). Right now it stands as a buyable residential lot (used to be a home business, but the owner was deleted using Theo's Simpe plugin).
Here's a pic of the "phenomenon".
Is this just a normal manifestation of the game I'd never witnessed before? If so what does it mean?
This is my main neighborhood (no subhood), I have all EPs ('cept M&G).