Interesting - I have not seen this in Baritone music either. (I've seen it in string music but the baritone can't shift hand position so it certainly doesn't mean that!!)
My best guess is that it means to cut off on beat 4 and beat 3, respectively, but that's just my initial interpretation based on the music. I wouldn't dream of putting that in as the way it should be interpreted. I think in this case you can use your judgement as to how you want to indicate it. Either as a footnote with a TN explaining at each instance or as a word sign expression in parentheses following the note. If you use parentheses, you may want to add a TN before the music saying that you've done that. Otherwise the reader will have no idea that it comes above the notes and is not enclosed in parentheses in print.
Hope that helps!
Kathleen