Protests seem to go hand in hand with G20 summits and usually on a fairly grand scale.
But one individual tried his luck by brandishing a placard in front of the summit conference hall.
Euronews reporter Seamus Kearney said he was expressing his anger over globalisation pollution when police pounced.
Seoul is obviously on a high security alert. South Korean police have created a no-go-zone of a two kilometres radius round the summit conference hall. It means the thousands of demonstrators who are expected to turn up will be kept well away from the talks.