I think those two examples are a bit over-the-top, but I wonder if there might be a benefit to having such a visible convention, partly just because it's such an obvious reminder to be explicit about tone. Seeing it communicates tone and communicates that the reader should also go through extra lengths to communicate their own tone.

Though specifically for "praise:", I'm a much bigger fan of the :+1: thumbs up emoji instead which accomplishes about the same thing.