The Texas Rangers came with smooth football targets.

Looking on K-frames that came with targets before late '79, they should all have "T" for target (like the N-frame posted earlier [by you ]) and those came with extractor relieved/football targets. When S&W went to the speedloader targets in late '70 it changed to ST.
When they went to the computer labels it became TS.

So, for your 9/81 Model 19 it means speed loader targets but on the 1973 TR, it means smooth targets.