We saw this sign often.
But the dogs were usually inside.
While we were walking in Tuscany we passed a paddock with a flock of sheep. Just like a number of others, but in this case four "sheep" detached themselves from the flock and raced towards us barking savagely. These were Maremma sheepdogs, specially bred to live with the sheep and protect them from wolves, or Australian tourists.
As they rushed up to gate I thought we would just pass by ignoring them ("They'll never come through the gate"). Hah! Two stayed with the flock and the two others wriggled under the gate and advanced, snarling. Now my dear wife is not too good with dogs (or indeed most things that go on four legs ands are bigger than a tortoise), so she went pale and walked steadily away while I turned to face the dogs, suggesting as politely as I could that they should leave, and poking my walking stick at them. They followed us for 50m or so, then broke off went back into the paddock and rushed up to the top gate to check that we weren't planning to double back and steal a few of their charges, like true Australian swagmen.
After that we payed more attention to the "Attenti al Cane" signs and I had some difficulty in coaxing Jeannie down one road that was marked with that sign.
Not too rash, now.