"No doubt the coin is something to be given to whoever is in charge of the treasure, and Masulipatam may be the place where it is hidden." "Yes, or it may be a password.

It reminds one of the forty thieves business.

You go and knock at the door of a cave, a figure armed to the teeth presents itself, you whisper in his ear 'Masulipatam,' he replies 'Madras,' or 'Calcutta,' or something of that sort, you take out the coin and show it to him, he takes out from some hidden repository a similar one, compares the two, and then leads you to an inner cave piled up with jewels." Mark laughed.
"Well, it is no laughing matter, Mark," the Squire went on seriously.
"The little comedy may not be played just as I have sketched it, but I expect that it is something of the kind.

That coin has to be shown, and the word 'Masulipatam' spoken to the guardian, whoever he may be, of your uncle's treasure.

But who that guardian may be or how he is to be found is a mystery.