rat poison

I have seen men pushing these signs around town a few times. There are huge rats here, like the size of a cat. The only thing I can compare it to are the sewer rats in NYC.
I have not seen rats in my current flat/building (knock on wood!). At my previous residence, I was scared when coming home in the night because the hairy things would be scurrying about (outside) from under the car park, darting here and there. I was always afraid it would run over my feet. They are at the train station/tracks often.