Bengaluru, Sept. 11 -- A person who goes by the name Rihan Rathod posts a video on his public Facebook profile, early morning on the second week of August. In the video, he displays his phone number, and stacks of Rs.500 notes stored in what looks like an aluminium trunk, the kind found in many Indian homes for storing clothes or grain. Two more containers, brimming with Rs.100 and Rs.200 notes, can be seen next to it.

Rathod picks up a stack of Rs.500 notes and feeds it into a cash counting machine. It whirs and flashes a number-96. He fans through the bundle to point out the serial numbers, then holds one note up to the light, the textbook way to check authenticity.

In another video, posted on Instagram, in the last week of August, a ...