Assume I own a property where parking is a premium, such as a beach house. What can I do to prevent people from parking in my yard rather than paying for municipal parking? What markings would be required to indicate that parking is not allowed? Assume this is not an easement, but truly personal property such as a driveway or lawn.
Florida law Chapter 715 says (excess verbiage deleted or paraphrased)
The owner ... of real property... may cause any vehicle... parked on such property without ... permission to be removed by a (towing company) without liability for the costs ...under any of the following circumstances: (conditions on the towing yard: must be nearby and open for business during reasonable hours).
As for notice, it depends on the nature of the property. No notice is required "for property appurtenant to and obviously a part of a single-family residence", and an exception exists if you personally give notice to the owner / operator ("personally" means "communicating with the person" so writing a note and sticking it on a car does not count). If it is not obviously part of a single-family residence, then there are a lot of conditions that have to be satisfied ("at each driveway access or curb cut allowing vehicular access to the property, within 5 feet from the public right-of-way line", "clearly indicate, in not less than 2-inch high, light-reflective letters on a contrasting background, that unauthorized vehicles will be towed away at the owner’s expense. The words “tow-away zone” must be included on the sign in not less than 4-inch high letters", "provide the name and current telephone number of the person or firm towing or removing the vehicles or vessels" etc.). My admittedly limited experience with the Florida coast is that it is never obvious that a piece of property is part of single-family residence, though I often suspect that it is. So you could take a chance and omit the sign, or you could get a sign.
If it is private property, then it is not mandatory for you to provide any notice at all - people who park on your property are trespassing, and it is their responsibility to stay off of private property.
But if you just want to make it extra clear that it is private property, then basically you are just asking what kind of sign makes it clear that parking is not permitted there... have you considered a "No Parking" sign? (Or a "Private Property" sign?)