In
King Ottokar's Sceptre (around p.34), in the royal jewels' room (first setting), a serpent-like dragon can be seen on the fresco, speared by St. George (one more avatar of Georges, after Varghese and Jorgen)...
see
http://en.wikipedia.org/wiki/Saint_George
Interestingly, other dragons can be seen in the
Blue Lotus (in the opium den) & in
Tibet (behind the Grand Abbot), namely in two settings connected with Tchang, with Dante's quotes ('Abandon all hope') and with 'abandoned characters' that might stand for a bygone writing system, in Tintin's unique world.
see
https://www.tintinologist.org/forums/index.php?action=search&loc=1&foru m=8&topic=1691&page=