Does hand gesture have an impact on meditation or attainment of Nirvana? The question regarding the gesture while sitting for meditation has always intrigued me. When I tried to ask this to a Vipassana teacher in my 10-day course, he put it off saying I should concentrate on meditation first without worrying about these matters. Does it mean that it doesn't make any difference?

I personally use the dhyana mudra (fore-finger touching the thumb in a circle, and other three fingers straight out) while sitting cross-legged. But in many of Buddha's statues, I've seen him keep the left hand over right, and in some others, thumb touching forefinger and hand kept straight across the chest gestures.

Want to know from advanced practitioners, what do the Buddha's postures indicate? More importantly, does having a certain gestures have any good or bad effect on our vipassana practice?
Yes and no.

Certain hand gestures cause better energy flow through your body and vibrations. These vibration can be some times an aid in dissolving pain and also fabrication.

If you get attached to the vibrations and gestures this will do more harm than good in your progress.

So my advice is do not bother too much about these as their contribution to your final goal is marginal or non existent through it might give a mild boost to better practice in certain situation is making you conferable to be seated for a long time by creating Piti which is one of the enlightenment factors but keeping in mind you cannot bake a cake with one ingredient and attachment to the feeling or creating view and perception around the gestures will hold you back