I'd guess as a deterrent, a realistic fake might be as effective...

One of our 4 cameras is outside but I'm not sure if it would be that readily spotted by someone calling at the house (L shaped bungalow). I opted for a more complete view of the front of the property than I'd get from the porch door area. That and I guess ease of fitting - a switch with POE does for the cabling to that one and the one in the living room. (The other 2 are 12v powered and one of them using wi-fi).