That looks like an object that isn't fully loaded (the white mesh before the texture is applied). I've never had a white plumbob in my game, though I've seen many items temporarily white while the game pulls up the textures.
Makes me wonder if you've had a sim glitch there somehow. Could be an invisible townie/homeless sim stuck there with a perpetual plumbob, or maybe a sim glitched in that spot and left a broken plumbob behind. You could try resetting all of the sims with the "resetsim *" code. You could also see if it's somehow attached to the lot by saving it to the library and placing a copy in a new game - if the plumbob is still there that means it's now attached to the building somehow.
