Hold up an index finger in the neutral fingerspelling position. The finger
is pointing up, the palm-side of the hand is facing forward. Make a twisting
rotational movement and end up with the palm-side of the hand facing
backward towards yourself. The movement is somewhat similar to running
your fingertip along the inside of an upside-down bowl of leftover frosting
so as to get some left-over frosting onto your fingertip (so you can stick
it in your mouth -- of course).
This version is commonly used to mean "just"
as in "there is just one left."
JUST / ONLY:
To sign this version of "only" hold an index-hand palm up (the
index finger is pointing up, the flat of the fingernail is toward
the viewer). Move the hand in a small horizontal circle as if
drawing a circle the size of a quarter on the underside of a table.
This sign also means "someone / something / single."