Ah, the famous "Watch out for Kangaroos" sign! How close to the city can you see it? Not far at all! This is Lane Cove National Park: as the crow flies, it would be no more than 5 km away from the city centre. Seeing the sign doesn't mean you will see the beast though. For that, try and come real early in the morning: if you're lucky you might spot one hopping away. By the time the picnicking crowds arrive, the mob will have disappeared deep into the bush.
And by the way, they aren't kangaroos here but wallabies, a smaller grey member of the family.