The original post, is pretty vague in that there is no hint as to which public buildings are being referred to.
To me, the principal question to be resolved is the exact definition of "carry".
Most of the statutes involved in this question use this definition:
175.60(1)(ag) “Carry” means to go armed with.
Notice the following paragraph, does NOT prohibit firearms. It prohibits you from
carry... You are not allowed "to go armed with."
175.60(16) PROHIBITED ACTIVITY. (a) Except as provided in par. (b), neither a licensee nor an out−of−state licensee may knowingly carry a concealed weapon, a weapon that is not concealed, or a firearm that is not a weapon in any of the following places:
Here is the DOJ FAQ summarized 175.60(16) list that is prohibited without a need for signage:
Any portion of a building that is a police station, sheriff‘s office, state patrol station, or the office of a Division of Criminal Investigation special agent of DOJ.
Any portion of a building that is a prison, jail, house of correction, or secured correctional facility.
The Sand Ridge Secure Treatment Center, the Wisconsin Resource Center, or any secured unit or secured portion of a mental health institution, including a facility designated as the Maximum Security Facility at the Mendota Mental Health Institute.
Any portion of a building that is a county, state, or federal courthouse.
Any portion of a building that is a municipal courtroom if court is in session.
A place beyond a security checkpoint in an airport.
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Another 11Act35 modified Wisconsin statute:
941.235 Carrying firearm in public building.
941.235(1) Any person who goes armed with a firearm in any building owned or leased by the state or any political subdivision of the state is guilty of a Class A misdemeanor.
(2) This section does not apply to any of the following:
...
(e) A licensee, as defined in s. 175.60 (1) (d), or an out-of-state licensee, as defined in s. 175.60 (1) (g).
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Here is the statute that involves sign posting or notification to deny the privilege to carry:
943.13 Trespass to land.
(1e)(aL) "Carry" has the meaning given in s. 175.60 (1) (ag).
...
(bm) "Licensee" means a licensee, as defined in s. 175.60 (1) (d), or an out-of-state licensee, as defined in s. 175.60 (1) (g).
(1m) Whoever does any of the following is subject to a Class B forfeiture:
This is followed by quite a few paragraphs, describing different property types, (single family residences, multi-family residences, non-residential buildings & grounds, Land, special events, state or local government buildings not in 175.60(16)(a), buildings on the grounds of universities or colleges, and the access rules that apply to these property types. All of these paragraphs that mention firearms, use the phrase
While carrying a firearm
go to the DOJ FAQ and look at the section on:
RESTRICTIONS BY BUSINESSES AND PROPERTY OWNERS page - 32 -
Again "Carry" is defined "to go armed with"
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I do not think someone who has a handgun encased and unloaded would be considered "to go armed with" a handgun.