Uhh, absolutely not. You wouldn't find a single person bobble their head if they were asked whether they'd like to get punched. Unless maybe they're a masochist.
It's often used as a reluctant yes, yes, "Yeah, I gotcha", and somewhat uncommonly an "I don't know" but it cannot be used as a no.
Never used it myself but I remember it from when I was a kid back when I lived in India.
In my experience people will use it when They are afraid to say no, Despite the answer being no.
For example for my work i have to train alot of indians. And if I'm covering a particularly hard topic, i will sometimes ask, "Do you understand?" and if their boss (my client) is in the room with them they will never shake their head no, they will instead bobble their heads and after training when their boss isn't present they will explain that they did not understand the topic and ask me to go over it one more time.
Other areas, if i ask an indian person if I pernounced their name correctly (and i didn't) - If they are working class they will most often bobble their head, while executives will more often than not be more vocal. Or gave a clear nod yes, or shake no.
This guy seems to say the same thing
http://www.youtube.com/watch?v=3hCV2oO2akw
So like I said, its not a "NO" emphatically. But sometimes it can be closer to "No" than "Yes"
More like "I want to say no, but i'm worried about the reaction i will receive so I will substitute this "NO" for a bobble. [and in my book that counts as a no]