The motto: Nec sorte, nec fato - Neither by chance nor destiny
The crest adorns the gate to the manor, above the main entrance to the manor itself, it's on a tapestry above the fireplace in the ballroom of the manor. Theo also has the family crest engraved in a ring he wears, which he uses as a seal. Hence any letter from Theo (unless he is trying to hide his identity) is sealed with the image of the crest (there are more seals, but until the day Theo marries, they are under firm lock and key).