There is some smell when girls are in heat , but it's not strong. Estrus urine attracts males to a female in estrus, odor stimulates sexual activity in males. My girl also raises her butt and goes backwards!
When chins are scared they can emit smell that is really strong. Sudden, loud or unfamiliar noise or movement can trigger it. I think chins in the wild communicate danger to each other through smell.I remember that once I took Lola out of the cage early in the morning(Chippy was in the cage), and then someone made a loud noise outside. She got scared and emitted the smell, in 3 seconds or so Chippy made very loud long cries. He was trying to tell do not hurt my girl!
During introduction, my girl was afraid of Chippy, and I felt the smell. Chippy started to chase her right after she did it.
And Chippy emitted the smell too when Lola was in heat( they were housed in different cages, he could not see her). I think he was trying to let her know he is near and ready, and maybe to let other chins know that this is his girl-stay away.
Chins have highly developed olfactory systems, they also have a Jacobson's organ in the roof of their mouth. It improves sense of smell.For the most part, their single most important exteroceptive sense is smell.
My boy Chippy is very territorial. Once I let Lola out of the cage first, for playtime. When it was Chippy's turn, he kept on smelling the floor pulling his lips back during smelling(his head was moving up and down).This facial expression(flehmen response) enhanced the sensitivity of the Jacobson's organ. Scent-marking is an important communication tool for them. Then he emitted an odor, maybe he was trying to mask Lola's scent.
So, I think there are several reasons why chins emit smell.
Interesting article:
http://www.cosmosmagazine.com/news/2150/mammals-emit-smell-signal-danger