The IPA uses the 5 tone-letters ˥,˦,˧,˨,˩. Unicode also has reversed (꜒,꜓,꜔,꜕,꜖) and dotted tone bars (꜈,꜉,꜊,꜋,꜌; ꜍,꜎,꜏,꜐,꜑). What are these characters used for?
Dotted tone letters*: Dotted tone letters are used in Chinese linguistics to indicate tones in certain weakly-stressed syllables having a less-distinct quality—there is little or no pitch variation, and the duration is short. These are often referred to in Chinese linguistics as “neutral tones” Although we call it a "neutral" tone (in Chinese it is called a "light" tone). It takes very little time to say, and does not hold or change its pitch. We use the voice-range stem (|) plus a dot to show where one's neutral tone should be.
With further material from Chinese Primer: Lessons
Reversed tone letters: In the same Comments on Proposal document, the author suggest using the left-stemmed tone bars in combination with the right-stemmed tone bars to indicate contours. I am not certain if this was a mere suggestion or was based on previous usage (Document is from 2003).
˥ = Top
˦ = High
˧ = Mid
˨ = Low
˩ = Bottom
The reversed and reversed dotted tone letters are referred to as Modifier Tone Letters too, the only difference is that they're called "left-stem". I think that considering the lack of info and references, we can simply consider them variations. Someone let me know if you find something, I've explored here and there but it really seems they have no particular use, concerning IPA.