I don't know if it meets the size requirements (can't tell what size it is), but if it does, then it's legally binding. You can't be arrested just for carrying, though. You have to be asked to leave. If you then refuse, they can call the cops and they'll remove you or cite you for trespassing.
Someone should put together an informational flyer on the downside of posting signs, i.e. that if something happens where a permit holder could have stopped a bad guy, but was prohibited from carrying, that he and other victims can sue. That might change some minds.
First part is semi-correct. You can't be "arrested" per-se for violating a legal sign in WI.
However, it's risky. WI does
not have the "Verbal warning/trespass authority if you refuse" for it's no-carry signs like many other states do. That, AFIAK, was in the old versions of the WI PPA bills that failed. I don't know exactly why it changed.
Failure to obey a proper no-CCW sign here is a $1000 WI state civil forfeiture. There's no requirement for the posted property owner to verbally notify, or warn someone who's in violation either.
The good news: a civil forfeiture is not even a misdemeanor, so your carry or gun-owner status, should not be in any jeopardy. The bad:
It's $1000-frickin dollars! And with no requirement to notify, someone who observes (or merely suspects) that you are carrying in violation of their sign, can call the po-po without warning as you browse in the store or whatever, and there's no "get out of it clause" like there is with the verbal warning/trespass states, where it's no harm-no foul if you willingly leave once instructed to do so.
So WI's signage enforcement is a mixed bag, there's zero criminal liability, but the fine is quite steep. And there's no way to weasel out of it by politely agreeing to leave the premises. Once you enter a posted location, the violation exists, and keeps on existing, even after you've left, if there's some credible proof, I guess. So if you're made in a posted location, they know who you are from some identifying information, like say, you used your credit card at the checkout, or someone got your license plate, they could still call the police after you've left, who might serve you with the citation at your home even.
It remains to be seen with how much zeal the police will follow up on this since the number of carriers who've gotten permits back is still just in the dozens. And it'll be interesting if local municipalities catch on, and create their own local civil forfeitures, to try and capture any revenue that the state would have otherwise gotten.
The upside though is they may set the fine lower than $1000.
The second part is dead-on though. WI's legislature thoughtfully added civil immunity over the actions of a licensed CCW'er to any business or public place that does NOT post. Any place that does post could face civil lawsuits if someone who has a CCW permit, and did not carry because of the signs, and is harmed in a crime or violent act on their property.
Hopefully the reality of this will be an incentive in the long run for most postings to come down, or not be replaced as they fade or wear out.
The sign I took a photo of above is legal, as it's printed on 8.1x11" paper. IIRC, the minimum size in the law is 5x7".
I haven't scouted my whole building yet, but we do share an "L"-shaped rear courtyard/loading dock area that I can see from my office windows. (I have a killer view of the dumpsters) and from what I see, they haven't posted all the entrances to their building, but they may still be legally covered, because I believe the law states "All entrances readily accessible by the public. And the rear service doors etc. aren't "common entrances" and presumably are secured and only accessed by the employees etc.
