Of course, aside from a rather trivial exception, this seems to be quite inaccurate. Whilst animals have been used in the past to denote dangers of the unknown (an Anglo-Saxon map warns of lions in Africa, Ptolmey's Geographia atlas warned of elephants, hippos and even cannibals!), the only instance where dragons were mentioned by name comes from the Hunt-Lenox Globe (which is actually on display at the New York Public Library).
|The Hunt-Lenox Globe (squint eyes to see Latin)|
Scholar Dennis McCarthy summarises the entire misconception well:
"The phrase was not, as so many believe, a general warning to sailors about alien realms. It was, instead, one of the first recorded post-Columbian biographical remarks and has now become, perhaps, the most famous distributional comment ever, likely marking the general region where tales of the Komodo dragon originated"References:
1. Dennis McCarthy (2009). Here be Dragons – How the study of animal and plant distributions revolutionized our views of life and Earth. Oxford University Press. ISBN 0-19-954246-5.