More dog signs! This sign was on the door of a bus in Tallinn. The sign starts by forbidding drinks, smoking, rollerblading(?) and bicycles. Then the rightmost part doesn't forbid but limits dogs as the dog is depicted having not only a leash hold tight, but also a muzzle. So the sign seems to imply that dogs are potentially dangerous?
On the other hand, the dog depicted in the sign seems to have floppy ears, and so I don't think that it is supposed to index a particularly dangerous dog. In particular, the idea seems to be that even "your harmless dog" needs to be controlled? Note also that the leash of the dog is held tight, and the dog is looking up in a way that seems subservient to me.
Maybe the idea here was that they want to allow dogs to enter, but to emphasize the need for control to people, and a muzzle is a very strong visual symbol for controlling a dog?