Brings to mind:
“Beware the Jabberwock, my son!
The jaws that bite, the claws that catch!
Beware the Jubjub bird, and shun
The frumious Bandersnatch!”
(from Jabberwocky by Lewis Carroll)
I suspect it might have something to do with the word "beware." Its usage might be different in different dialects. I would always use it as a phrasal verb "Beware of the dog." It seems incomplete to say "Beware the dog."