These 'reversed' tone letters are used to indicate tone sandhi. For example, ˧꜖ after a word or syllable indicates that it has a mid tone in isolation, but a low tone in the current environment.
When this symbol occurs in combination with other tone letters, they indicate the pitch contour of the tone. For example, ꜖ means a level extra-low tone, and ꜕꜖꜓ means one that begins low, then goes extra-low and ends high.
Tone letter on Wikipedia.Wikipedia 