Occasionally a setter may see that a part of a word is a mirror image of itself and so can indicate this using a reflection indicator.
Here is an example:
The setter wants to make the word AMMA (an Indian term for mother) and sees that AMMA is AM reflected and so the setter may write simply:
am reflected = AM + MA
am mirrored = AM + MA
This indicator is not widely used (perhaps because actual reflections change the appearance of letters and often make the clue appear inaccurate) but I include the clue-type for completeness.
Here is an example of one at work:
Jazz fan reflected during very choppy performance (8)
jazz fan - cat
reflected - reflection indicator
during - insertion indicator
very - so
choppy performance - definition
S(TAC<>CAT)O = STACCATO
Note that the A & T of the reflection works fine, but not the C as it is not a symmetrical letter. Some would say that this makes the clue unfair.