These 'reversed' tone letters are used to indicate tone sandhi. For example, ˧˥꜔ after a word or syllable indicates that it has a rising tone in isolation, but a high 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 mid tone, and ꜕꜖꜔ means one that begins low, then goes extra-low and ends mid.
Tone letter on Wikipedia.Wikipedia 