What does "m.Iz." or "m.Tz." (or "m.I%." or "m.T%.": I don't know if it is a "%" or a "z") mean in this score? The piece is the waltz "Diana Triste" of the Colombian composer Luis A. Calvo (1882-1945). Here is the link to the score:
My guess is that this is a Spanish score?
If so, the abbreviations tell us which hand plays which notes.
The "m.Iz." stands for "mano izquierda," which is Spanish for "left hand." The "m.d.," meanwhile, stands for "mano derecha," or "right hand."
The upper staff in the second-to-last measure, for instance, will switch hands every beat as you climb up the keyboard: right hand on beat 1, left hand on beat 2, and right hand on beat 3.
Similar terms are used for scores in other languages; see Why is there a "G" marked on an augmented octave in Scarlatti Sonata K466 in F minor?
If I where sight-reading this, the conductor would have received
b/c I'm also looking at the scoop next to the birds-eye.
Medium Trillz is my answer since I go the Italian language on sheet music before any spanish begins to cross my mind.