Turns out that “Beware of Dog” signs are nothing new. The above preserved tile mosaic from Pompeii is one of the oldest dog warning signs in existence. The sign features an image of a dog and the words “Cave Canem” which loosely translates to “caveat” (beware) and “canine” (dog).
The mosaic can be seen at the House of the Tragic Poet, a Roman house in Pompeii, Italy dating back to the 2nd century BC. The house is famous for its elaborate mosaic floors and frescoes depicting scenes from Greek mythology. [source]
Discovered in November 1824 by the archaeologist Antonio Bonucci, the House of the Tragic Poet has interested scholars and writers for generations. Although the size of the house itself is in no way remarkable, its interior decorations are not only numerous but of the highest quality among other frescoes and mosaics from ancient Pompeii. Because of the mismatch between the size of the house and the quality of its decoration, much has been wondered about the lives of the homeowners. Unfortunately, little is known about the family members, who were likely killed by the eruption of Mount Vesuvius in 79 AD. [source]