Interesting...can you cite the particular law or code?
In Utah that standard is: IF there is NOT a Law making something ILLEGAL it is by definition LEGAL.
Many in the Utah forum have looked and have been UNABLE to find ANY law that would make ANY sign on ANY location OTHER THAN Certain specific locations such as a Courthouses, secure portions of Jails, secure portions of Mental health facilities, Secure portions of an airport, schools, Federal properties and post offices (last 2 based on Federal Statues). certain Churches may prohibit by sign or other options (infraction) and a sign or verbal notification at a private home.
http://le.utah.gov/~code/TITLE53/htm/53_05_071000.htm
53-5-710. Cross-references to concealed firearm permit restrictions.
A person with a permit to carry a concealed firearm may not carry a concealed firearm in the following locations:
(1) any secure area prescribed in Section 76-10-523.5 in which firearms are prohibited and notice of the prohibition posted;
(2) in any airport secure area as provided in Section 76-10-529; or
(3) in any house of worship or in any private residence where dangerous weapons are prohibited as provided in Section 76-10-530.
Amended by Chapter 366, 1999 General Session
The most that they could ATTEMPT to pursue someone who REFUSED TO LEAVE for whatever reason when asked to leave would be a criminal trespassing charge. Look closely at the defense to prosecution (4) (a) and (b).
http://le.utah.gov/~code/TITLE76/htm/76_06_020600.htm
76-6-206. Criminal trespass.
(1) As used in this section, "enter" means intrusion of the entire body.
(2) A person is guilty of criminal trespass if, under circumstances not amounting to burglary as defined in Section 76-6-202, 76-6-203, or 76-6-204 or a violation of Section 76-10-2402 regarding commercial obstruction:
(a) the person enters or remains unlawfully on property and:
(i) intends to cause annoyance or injury to any person or damage to any property, including the use of graffiti as defined in Section 76-6-107;
(ii) intends to commit any crime, other than theft or a felony; or
(iii) is reckless as to whether his presence will cause fear for the safety of another;
(b) knowing the person's entry or presence is unlawful, the person enters or remains on property as to which notice against entering is given by:
(i) personal communication to the actor by the owner or someone with apparent authority to act for the owner;
(ii) fencing or other enclosure obviously designed to exclude intruders; or
(iii) posting of signs reasonably likely to come to the attention of intruders; or
(c) the person enters a condominium unit in violation of Subsection 57-8-7(7).
(3) (a) A violation of Subsection (2)(a) or (b) is a class B misdemeanor unless it was committed in a dwelling, in which event it is a class A misdemeanor.
(b) A violation of Subsection (2)(c) is an infraction.
(4) It is a defense to prosecution under this section that:
(a) the property was open to the public when the actor entered or remained; and
(b) the actor's conduct did not substantially interfere with the owner's use of the property.
Amended by Chapter 334, 2010 General Session
Download Code Section Zipped WordPerfect 76_06_020600.ZIP 2,869 Bytes
More to follow....
Edited to add the following:
The Utah State Legislature has restricted ANY other entity be they State level, city, or municipal from imposing possession or carry restrictions MORE restrictive than state law WITH EXPLICIT legislative action authorizing it. Counties DO NOT have the authority to even restrict the discharge of a weapon! The authority to restrict the discharge of a firearm is given to Cities, Towns, or Municipalities ONLY.
http://le.utah.gov/~code/TITLE53/htm/53_05a010200.htm
53-5a-102. Uniform firearm laws.
(1) The individual right to keep and bear arms being a constitutionally protected right under Article I, Section 6 of the Utah Constitution, the Legislature finds the need to provide uniform civil and criminal firearm laws throughout the state.
(2) Except as specifically provided by state law, a local authority or state entity may not:
(a) prohibit an individual from owning, possessing, purchasing, selling, transferring, transporting, or keeping a firearm at the individual's place of residence, property, business, or in any vehicle lawfully in the individual's possession or lawfully under the individual's control; or
(b) require an individual to have a permit or license to purchase, own, possess, transport, or keep a firearm.
(3) In conjunction with Title 76, Chapter 10, Part 5, Weapons, this section is uniformly applicable throughout this state and in all its political subdivisions and municipalities.
(4) All authority to regulate firearms is reserved to the state except where the Legislature specifically delegates responsibility to local authorities or state entities.
(5) Unless specifically authorized by the Legislature by statute, a local authority or state entity may not enact, establish, or enforce any ordinance, regulation, rule, or policy pertaining to firearms that in any way inhibits or restricts the possession or use of firearms on either public or private property.
(6) As used in this section:
(a) "firearm" has the same meaning as defined in Subsection 76-10-501(9); and
(b) "local authority or state entity" includes public school districts, public schools, and state institutions of higher education.
(7) Nothing in this section restricts or expands private property rights.
Renumbered and Amended by Chapter 382, 2008 General Session
AND
http://le.utah.gov/~code/TITLE76/htm/76_10_050000.htm
76-10-500. Uniform law.
(1) The individual right to keep and bear arms being a constitutionally protected right, the Legislature finds the need to provide uniform laws throughout the state. Except as specifically provided by state law, a citizen of the United States or a lawfully admitted alien shall not be:
(a) prohibited from owning, possessing, purchasing, selling, transferring, transporting, or keeping any firearm at his place of residence, property, business, or in any vehicle lawfully in his possession or lawfully under his control; or
(b) required to have a permit or license to purchase, own, possess, transport, or keep a firearm.
(2) This part is uniformly applicable throughout this state and in all its political subdivisions and municipalities. All authority to regulate firearms shall be reserved to the state except where the Legislature specifically delegates responsibility to local authorities or state entities. Unless specifically authorized by the Legislature by statute, a local authority or state entity may not enact or enforce any ordinance, regulation, or rule pertaining to firearms.
Enacted by Chapter 5, 1999 General Session
Look closely at 53-5a-102. Uniform firearm laws. part (2)(a)and (b)
(2) Except as specifically provided by state law, a local authority or state entity may not:
(a) prohibit an individual from owning, possessing, purchasing, selling, transferring, transporting, or keeping a firearm at the individual's place of residence, property, business, or in any vehicle lawfully in the individual's possession or lawfully under the individual's control; or
(b) require an individual to have a permit or license to purchase, own, possess, transport, or keep a firearm.
Plus
(5) Unless specifically authorized by the Legislature by statute, a local authority or state entity may not enact, establish, or enforce any ordinance, regulation, rule, or policy pertaining to firearms that in any way inhibits or restricts the possession or use of firearms on either public or private property.
.... if they said "trespass them because they have a firearm" the local authority (Police, Marshal, or Sheriff ) IS PROHIBITED BY STATUTE FROM ENFORCING ANY SUCH "...Ordinance, regulation, rule, or policy pertaining to firearms that in any way inhibits or restricts the possession or use of firearms o either public or private property."
Again, the above is all applicable to UTAH only.