Reading more and looking at the picture blown up, could that be a triangle printed on the coin? The Fateful Coin is described as:
Description: The thick silver coin has a red triangle on one side and a red pentagram on the other. Engraved on the coin are letters in an ancient script.
When activated (but only after it's flipped), the coin emanates a silver glow briefly, and scarlet-hued script flickers in and out of existence in the air surrounding the coin as it falls to the ground. It sounds as a normal coin would when it hits a hard surface.
The picture seems to match the description. The "smoke" could be the silver glow? The coin in the picture does seem to have letters in an ancient script around the edge that is glowing reddish, though the pictures doesn't show any script flickering in the air surrounding the coin.
Oops. Reading on, I see: "Finally, the coin does not allow itself to be removed from a temple of Tyche." If that's the case, this isn't the coin.
There is a coin in
Ruins of Undermountain that bursts into flames when held enveloping the holder in a 2' pillar of flame and will then burn down through anything for miles. So, that probably isn't the coin he holds.
That's all I can find that seems close to being a fit.