|Place of Origin|
The Sebastian's Symbol is a lion in which he chose himself since bastards don't belong to a house. Therefore having the free choice of representation.
In Fated, Bash tells Mary Stuart that bastards get to choose their own symbol and that he chose the lion. He shows her his sword and tells her that Tomas likely chose his own as well. Mary recalls the dragons on his ships. Meaning that Nostradamus' prophecy about the lion fighting the dragon on a field of poppy's. Really meant that Bash faught Tomas. She then starts to believe in Nostradamus' prophecies.