！
Beware of the dog!
Literal
Vicious-dog [to-に] beware!
The famous warning sign text — one you'll see on Japanese front gates. ~に注意 ('pay attention to X, beware of X') is a fixed warning frame used without a verb. 猛犬 is the compound for 'fierce dog,' literally 'ferocious dog.' Strict signage style omits the polite verb, relying on the noun phrase to convey the warning.