The concept of "-ish" (as in "approximately") can be shown by
dominant "5-hand" in a circle (sort of like washing a
wall) while using a
facial expression that looks like you are estimating something in your mind.
APPROXIMATELY / about / around / -ish:
If you mean "-sh" as in "3 o'clock-ish" (or "Around 3 o'clock") you would do the
sign for "3 o'clock" and then wiggle the 3 side to side a bit as you hold it up.
You would also use a "mitigating" facial expression wherein you show the
uncertainty of the time in your face.