How to spot a fake currency note

How to spot a fake/counterfeit currency notes.
Mid-day tells you how - Read this: How to spot a fake Gandhi

This reminds me of a joke that my friend used to tell when I was in college.
Friend: Maga, how sure are you if the 100 Re. Note you have is genuine and not a fake?
Me: Pretty sure, (I hold it up) see there's a silver line, a watermark....
Friend: tut tut, there's an easier way.
Me: cool, how??
Friend: First, you Fold the note like this... (Folds it in half widthwise and then into lengthwise)
Now, hit the note with your fist, like this... (Hits it hard)
Unfold it and check if Gandhi's glasses (spectacles) are broken.
If it has, its fake else… enjoy!!
Me: hmm, Now, I am going to kick your A**....
Friend: *^&# &^%

Also, check the Reserve Bank of India for more info.