Plumbob is part of anatomy of a sim?

This is the question, and also my theory

Plumbob is really part of a sim, instead be only a visual effect to say us this is the active sim

Get to Work and other expansions let me say it
With GtW we have an illless called irritated plumbob, and at Get Together at plumbob is the icon of the club. Of course also with Vampires we have an vampire indicator (a different plumbob?) if the sim is vampire or become vampire

Then, is the plumbob part of a sim?