Making a Circling Motion
of the Index Finger at the Ear
=Finger Spinning around the Ear

It signifies that  the person is crazy  or is speaking nonsense. But, in In Argentina, it means 'you have a call.’

Jimmy: (making a circling motion of the index finger at the ear) "Did you hear about Mark's latest idea?"

RM    : "Yeah, I did. Sounds a bit crazy, right?"

Jimmy: "Completely! I can't believe he thinks it'll work."

RM    : "Well, you know Mark always full of funny plans."