Plumbob

Plumbob
A PlumbBob is used in most titles of the Sims series to identify the character selected. It is also used to show the mood of your Sim.

Plumbob in the Sims 2
In The Sims 2, the plumbbob is white if the Sim has a very high mood, bright green if the Sim's mood is high, bright red if it is low, or if mood is somewhere in between then it will be a shade of green-yellow reflecting the approximate level.The PlumBob is featured through all Sims games and in The Sims it barely ever changes.

Perma-platinum can be achieved through completing the Sim's Lifetime Want if the player has Nightlife through Bon Voyage, however if the player has FreeTime perma-platinum can be reached through completing the life achievement bar.

Also in The Sims 2, Sims who belong to the same active group as the selected Sim will have a smaller plumbbob over their head. This plumbbob is blue, irrespective of mood.

Plumbob in The Sims 3 (with World Adventures)
In the Sims 3 with The Sims 3: World Adventures the plumbob is green if everything's right, and red if the sim is in bad humor and has bad moodlet or low needs. There is a colour introduced by World Adventures: yellow. It is the subject of speculation, one thinks that it means the sim is in an "adventurous" mood, but the most important part of the people thinks that it is a mood between green and red, maybe as in The Sims 2.

Plumbob to a Sim
According to the "Atlas's Burden" statue in The Sims 3, the PlumBob is a tangible representation of the "celestial weight" (the player) controlling the Sim's world.