I am not sure why you want to focus on the County in this discussion of public office campaign signs relative to the HOA Act when HOAs typically are much more restrictive than the County when it comes to signs. 

Not to mention that I am not sure to what extent county can even  regulate political signs on private property given the SC ruling that political signs are a form of political speech. See below:

SUMMARY

The U.S. Supreme Court has ruled that the display of political and other types of signs on residential property is a unique, important, and protected means of communication and towns cannot restrict the display of such signs. The decision has not been overturned. In a 1994 case, the Court upheld lower court rulings declaring an ordinance that bans residential signs an unconstitutional restriction on the freedom of speech (City of Ladue, et al. v. Margaret P. Gilleo, 114 S.Ct. 2038). The Ladue, Missouri ordinance banned all residential signs (with some exceptions) to minimize visual clutter in the town. A resident sued, alleging that the ordinance violated her right to free speech by prohibiting her from displaying a sign stating “For Peace in the Gulf” from her home. The District Court found the ordinance unconstitutional, and the Court of Appeals affirmed. The Supreme Court agreed, finding that the town's interest in regulating signs does not outweigh its residents' right to free speech. 

The Court's decision holds that signs are an important medium of political, religious, or personal messages for which there are no exact alternatives. Handbills or newspaper advertisements are poor substitutes since a residential sign readily identifies the “speaker.” Yard signs are unusually inexpensive and convenient. They are a particularly effective way to reach one's neighbors. Moreover, the Court recognized the special place that individual liberty in the home holds in our culture and our law. While signs are subject to municipalities'police powers, the Court warned that they affect communication and towns cannot be overbroad in their restrictions on free speech.