I've seen commentators use this symbol at the end of their analysis but I don't know what it means. Does anyone know?
Descriptive Notation. It is an alternative notation for recording chess games.
Descriptive notation is a notation for recording chess games, and at one time was the most popular notation in English- and Spanish-speaking countries (Brace 1977:79–80) (Sunnucks 1970:325). It was used in Europe until it was superseded by algebraic notation, introduced by Philipp Stamma in 1737.
The abbreviation TR seems to refer to the spanish descriptive notation:
The initials are taken from the equivalent Spanish words: dama for queen, rey for king, torre for tower (i.e. rook), caballo for horse (i.e. knight), alfil for bishop and peón for pawn. The files are named after the initials of the pieces on the back rank, with those on the queen's side being suffixed by the letter "D" and those on the king's side suffixed by the letter "R". From left to right along the back rank, this gives: TD, CD, AD, D, R, AR, CR, TR.