Very curious about the blue "plumbob"..

[Penguin]

Can anyone tell me what the blue plum bob means?
Scenario; My Sim is on a date, they've just arrived at Banzai Fuzion Bar. They're talking to one another and then suddenly a lite blue plumbob appears and it's like making a circular motion above their heads. What is that? 

[Deklitch]

That means that they are part of a group. When the blue plumbob becomes a pair of love hearts, that is the date symbol.