Can the state/county post No Trespassing signs for private property?

Question

There's a county park with some hiking trails near our house that my wife and I like to walk through in the mornings. We walk along the public road to get to the park, hike the trails, and return home via a wash (dry riverbed) that runs behind the park back towards the main road. We, and several other neighborhood residents, have been doing this for years.

Recently we had an encounter with a nearby resident claiming that we were trespassing on private property as were walking through the wash. We checked the property records, and indeed, there are two parcels of private land through which we were crossing to get back on the main road. Both parcels are vacant, unmarked, not fenced, and not owned by any of the nearby residents.

I'm not overly concerned with this person's claims as we aren't entering their property, but yesterday we found two posted signs in the wash at the park boundary stating: Private property. No public access. The signs were apparently installed by the county and seem legitimate with county seal and all. My question is, do these signs constitute reasonable notice (as described below) since they were not posted by the private landowners?

Arizona Revised Statute 13-1502 states (emphasis mine):

13-1502. Criminal trespass in the third degree; classification

A. A person commits criminal trespass in the third degree by:

1. Knowingly entering or remaining unlawfully on any real property after a reasonable request to leave by a law enforcement officer, the owner or any other person having lawful control over such property, or reasonable notice prohibiting entry.

2. Knowingly entering or remaining unlawfully on the right-of-way for tracks, or the storage or switching yards or rolling stock of a railroad company.

B. Pursuant to subsection A, paragraph 1 of this section, a request to leave by a law enforcement officer acting at the request of the owner of the property or any other person having lawful control over the property has the same legal effect as a request made by the property owner or other person having lawful control of the property.

C. Criminal trespass in the third degree is a class 3 misdemeanor.

The words on the sign are clear enough, but can the county speak for the owner of the vacant lots who, as far as I'm aware, don't know or care about what's going on? Is there any room to interpret the sign as simply a park boundary leaving the owners of the adjacent property to post their own "no trespassing" signs as they feel necessary (or not)?

Follow-up question: If the sign does constitute an enforceable, reasonable notice, would the private property owner(s) have to get involved for trespassing charges to be filed?

Answer 1

The county can certainly post a sign on the edge of the county property, informing people that what lies beyond is private property, and no permission to pass has been granted. Unless this was endorsed by the property owner or the owner's agent, I don't think this would constitute the "reasonable notice" mentioned in 13-1502 A 1 (quoted above) needed to make entry count as criminal trespass. If the property owner authorizes the county to post notices, that is of course different.

I don't see how the county can be considered a "person having lawful control over such property" but the law does not say that "reasonable notice" must be given by an owner or owner's agent, indeed it does not say who may or may not give such notice. I wonder if there is caselaw on the point.

Since the law makes a request from a law enforcement officer, who could be acting with no authorization from the owner, one of the possible conditions for criminal trespass, I don't see that the owner would need to participate in a trespass action.