In modern usage, beware is an uninflected verb meaning “to be cautious or wary.” Its most common use is as a verb in the imperative:
Beware of the dog. or Beware the dog.
Beware of scams.
Beware your girlfriend when he’s around!
No noun form for beware appears in either the OED or the Merriam-Webster Unabridged. Nevertheless, all over the web a plural noun form “bewares” occurs in titles and in headlines:
‘bewares’ For Bettors
Bewares and Background Check
Bewares of Copper Domination
Internet Freebie Bewares & How to Deal with them
Some writers are also giving the verb a long-obsolete third person inflection:
Indian army bewares its men of Facebook, Orkut
He meets enemies he bewares of.
Whether sorrowful or sassy, the poems in this new collection bear McHugh’s signature: a lively love for the very language she bewares.
She bewares her Suitors’ parents that she has even danced in bachelors’ parties.
But she bewares of telling all of it for the sake of the public
I found one headline example in which the imperative seems to have had an s added to it:
Bewares the pitfalls of property development
Writers looking for a high class synonym for the word warning, can always use caveat [kăv’ē-ät’, kä’vē-ăt’) ]. Originally a legal term, in general usage caveat has the meaning of “warning”:
Audit Finds $300 Million Surplus but Issues Caveat on School Finances
MacAddict issues CD-ROM caveat
DSi Wi-Fi Caveats and Issues
EPA Issues Caveat Emptor on H1N1 Disinfectants
NOTE: The Latin expression caveat emptor means “let the buyer beware.”
Depending upon context, here are some alternatives to consider before using “beware” as a noun:
Of course, there’s always good old warning.