Better than a sign,
get a water bowl made for a commercial kennels or veterinarian clinics. Something that holds about 5 gallons. Paint the name "Killer" on it, along with a doggy footprint that's the size of a cantelope.
Put a logging chain with 3/8 inch thick links on your front porch and have a 30" circumference studded collar attached to it. The other end should be welded to a stake that is pounded into the front lawn near the porch.
(But not a regular tent stake or land surveying stake--- I mean the entire driveshaft of a Chevy C 10 pickup truck driven into the ground like a 5 foot long stake.)