empty chair, empty stool. 空椅子, 空凳子

GETTY IMAGES
An image of his empty chair has been inspiration for artists - such as in this work by Badiucao.
Liu Xiaobo: The Chinese dissident memorialised in social art - BBC News
http://www.bbc.com/news/world-asia-china-40591147

Liu Xiaobo: His Name Will Be Remembered - CNN.com
http://edition.cnn.com/2017/07/14/opinions/liu-xiaobo-remembered-oped/index.html