indian 10-rupee coin
The mintmark is featured at the bottom on the obverse of the ₹10 coin. 
The first ₹10 coin minted in 2005 had a diameter of 27 mm and featured the lettering “भारत” and “INDIA” on the top, with Lion capital with ‘Satyameva Jayate’ in Hindi below at left, and the date of mint below it on the obverse. On the reverse of the coin it featured the “Four heads sharing a common body” – cross with a dot in each quadrant in the center, with the lettering “दस रुपये” and “TEN RUPEES” on the outer ring.  
It also added, It has come to the notice of the Reserve Bank of India that in certain places there is reluctance on part of traders and members of the public to accept Rs 10 coins due to suspicion about their genuineness.
He further added, “The banks accept the coin but they also hesitate to take-in large numbers of it.”
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Mintmark is on Obverse, below date.
Government announces new Rs 20 coin: Things to know
Confusion continues over Rs 10 coins, local shops reject tender
PM Narendra Modi inaugurated the new series coins.
The government released new Re 1, Rs 2, Rs 5, Rs 10 with refreshed design and attention towards the visually impaired citizens. The government has also issued new Rs 20 coins. Coins in this new series have been designed by the National Institute of Design with several differentiating features to make it easier for visually-impaired individuals to identify them. Not only distinctive markings, the coins will now get bigger and weigh more with the increase in denomination to make recognising them easier.