(Cheryl of the Clue Crew compares a logo with its antecedent.)  This association adapted the Duke of Lorraine's emblem because they, too, were fighting a crusade, but against tuberculosis
During ... 
Dr. Gilbert Sersiron of Paris suggested that as it was a crusade, the emblem of a 
... and the double-barred cross became the worldwide sign of the fight against TB
.