It is details from the top of the torch flame. Place another dime over it with the reverse facing up but turned topside down. That is how the reverse looks when the obverse is right side up. You will be able to see where those details came from.
I'll go with a die erosion pit. It looks similar to the anomaly on a dime I had a question about a couple weeks ago. https://www.cointalk.com/threads/1989p-dime-weak-strike-die-damage.259713/ It doesn't match the torch to be a clash.
http://www.errorvariety.com/Clashes/Roosevelt.html Here's an overlay of a die clash Roosevelt and nothing that would clash matches up with your Dime. Still pretty cool find it's not PMD so I'd keep it.
If it is in relief, I would be inclined to believe it was a polished out clash. There are alot of other marks on this coin as evidence of that. The picture of the whole obverse shows polished places at the artist initials and under ST in TRUST. It also appears to be an olive sitting on the bridge of his nose. This is my go to overlay.
