“Beware of (the) dog. And the cat is not trustworthy, either” is a jocular sign that has been printed on many images. “Beware of the dog. And the cat is not trustworthy either!” was printed in the Sun Times (Owen Sound, ON) on October 19, 2000.
 
 
19 October 2000, Sun Times (Owen Sound, ON), “Still sitting with my feet up” by Dave Carr, pg. A4:
“Beware of the dog. And the cat is not trustworthy either!”
       
Newspapers.com
7 May 2004, Pensacola (FL) News Journal, Pelican sec.,  “San Roc Cay Hosts Grand-Opening Event by Angie Fuller, pg. 32, col. 5:
Titles by Stone Sense are quite popular, and each has different words of wisdom to impart. Examples include “Beware of the dog, and the cat is not trustworthy either” and “When in doubt, add more wine.”
 
Google Groups: soc.culture.irish
Re: KateH for President 2004
kateh
5/19/04
(...)
Not bad.
Right now the warnings outside simply read :
On the garden gate : “Beware of dogs and the cat is not trustworthy either”
On the back door : “Forget the dog…Beware of Wife”
And at the front door : “Ask not for whom the dog barks…...it barks for
thee”
   
Google Groups: alt.lifestyle.all-faiths
wise words
PuNx
8/22/04
(...)
“Beware of the dog….the cat is not trustworthy either.”
   
Twitter
Krissy Johnson
@awesomefied72
“Beware of the dog… and the cat is not trustworthy either”
10:30 AM · Nov 10, 2008·Twitter Web Client
   
Twitter
Kendra Nichols
@kelynn
Just saw a sign that said ‘beware of dog. The cat is not trustworthy either’
7:47 PM · Jun 18, 2009·Twitter SMS
   
Twitter
Stephanie Williger
@MissStroup
Best sign ever: “BEWARE of the Dog. The Cat is not trustworthy either.”
1:52 PM · Jul 2, 2009·Twitter SMS
 
The Ledger (Lakeland, FL)   
Woman, 74, Has Rescued More Than 10,000 Muscovy Ducks
By ELINOR J. BRECHER / THE MIAMI HERALD
Posted Nov 19, 2011 at 10:44 PM
MARGATE | From the street, Eunice Sivertsen’s modest, 1960s-era Margate tract house seems unremarkable, though it’s clear she loves animals.
 
Whimsical woodland and barnyard-creature statues inhabit the lawn. A sign by the front door reads: “Beware of the dog. And the cat isn’t trustworthy either.
 
Twitter
FFZazzlesBest
@FFZazzlesBest
Beware the Dog T Shirt: Funny text tee says Beware of the Dog. The cat’s not trustworthy either. http://tinyurl.com/nxgupb3
7:01 AM · Jan 22, 2014·twitterfeed
     
myhorrynews.com
Business Profile | The Wacky Rabbit in Myrtle Beach both functional, beautiful
By Ettie Newlands .(JavaScript must be enabled to view this email address) Feb 4, 2015
(...)
Dog and cat lovers aren’t left out either, as indicated by the stone wall hanging that reads, “Beware of the dog. The cat is not trustworthy either.”
   
Google Books
Still on Record – The Return of the Archivist
By Berwick Coates
Paragon Publishing
2018
Pg. 213:
Beware of the Dog
The Cat is not trustworthy either
 
Twitter
Boarding Soon
@boardingsoon
Replying to @RJBrandenburg and @thespybrief
I have a magnet that says “beware of dog…and cat isn’t trustworthy either”.
9:52 AM · Jan 16, 2020·Twitter for iPhone