1957 D Wheat Penny- T On Rim

It looks like the rim above the T just took a hit. Also Trust is a little weak, maybe due to grease in the die.

I agree this is not a dropped letter error.

When debris, (often referred to by error collectors as "grease"), clog a die, it may after a few strikes, become compressed within cavities of the die such as numerals, letters or even areas of design. Even after the offending material has been dispersed from the field of the die through the striking of coins, it may remain intact within these recesses. Later the offending material falls out intact, like Jello from a mold, and becomes struck by the obverse die into the next coin. The result can be a perfectly shaped incuse letter struck into the coin with a bit of the offending material still retained sometimes. These type of errors are always sought after and carry a premium even as they are found more commonly than the past which is a good thing for coin searchers.

Heres a few: http://goccf.com/t/442928 and
https://coins.ha.com/itm/errors/200...0151-91499.s