As no state is specified in the question, I choose to discuss the law in maryland, as well as general common-law principles.
In the case of Frank SAMUELS v. James D. TSCHECHTELIN et al. No. 2044, Sept. Term, 1999. (Court of Special Appeals of Maryland.) 763 A.2d 209
The court said, quoting past cases::
To establish a prima facie case of defamation when the plaintiff is not a public figure, the plaintiff must prove: (1) that the defendant made a defamatory communication to a third person; (2) that the statement was false; (3) that the defendant was at fault in communicating the statement; and (4) that the plaintiff suffered harm. Thacker v. City of Hyattsville, 135 Md.App. 268, 313, 762 A.2d 172, 196 (2000); Rosenberg, 328 Md. at 675, 616 A.2d 866; Bagwell, 106 Md.App. at 510-11, 665 A.2d 297.
See also "Defamation Law in Maryland where the same elements are stated, citing Hosmane v Seley-Radtke, 227 Md. App. 11, 20-21 (2016)
Thuds it is an essential element of a defamation calm "that the defendant made a defamatory communication to a third person"
While it is a general principle of common law that:
The basic rule is that everyone involved in any way in the production or dissemination of defamatory material is liable as having published it.
according to the Wikipedia article "Innocent dissemination". That article goes on to say that:
At common law, a defense of innocent dissemination is available to a person who, neither knowingly nor negligently, had merely a subordinate role in the dissemination of the matter containing the defamatory statement.
This applies when:
- the defendant did not know that the publication complained of contained a libel;
- the defendant had no grounds to suppose that it was likely to contain defamatory matter; and
- the absence of knowledge was not due to any negligence on the defendant's part.
It would seem that on the facts assumed in the question the landowner has Arguably not made the defamatory statement at all, nor has she distributed or published it. She has merely failed to remove it from her property in as prompt a manner as she might have. Even if failing to remove the statement is considered to be a from of distributing the statemetn, it seems at least possible that a defense of innocent infringement would apply. I can find no court case at all closely on point, and the basic elements of defamation law in Marylnd seem to be common-law rather than statutory.
These are generally local or municipal rules. I could not find documentation for a typical rule in Maryland. I was formerly somewhat involved in public affairs, particularly in connection with lawn signs, political and otherwise, in the township of West Windsor, NJ.
There such signs could nort be placed so close to a roadway as to ovstruct teh sight-lines of drivers. Temporary signs in conection wiuth an event were required to be removed within 7 days after the date of that mevent. For political signs that was the eleection involvved. ll of this is contained in the township code section § 200-152 Temporary signs Subsection B (1) provides that:
Temporary noncommercial, including political signs. Noncommercial signs, including but not limited to political signs which are temporary in nature, shall be permitted in all districts. Temporary noncommercial signs are those which are not permanently affixed to the ground, a building or other permanent structure on the property and not intended to be permanent in time. Temporary noncommercial signs shall not exceed 16 square feet (no side of any signs shall be more than six feet in any linear dimension) in residential zones and 32 square feet in nonresidential zones. Temporary political signs associated with an election shall be removed no later than seven days after the election. Site plan approval shall not be required for the placement of temporary noncommercial signs.
The details of such rules will vary widely with the locality, but generally will require the owner to remove signs within some period of time if the person placing the sign without permission does not. But they are not likely to hold the owner liable for the sign having been places in the first place.