I practiced law in Hendricks County for 16 years before coming to Tennessee, the sign would act as notice that if you are armed, you are not permitted on the property and therefore they need not give any other prior notice. I believe that most LEOs would interprete those signs in that manner.
I agree that it could be interpreted that way.
Here are a couple of snippets of the statute in question:
IC 35-43-2-2
Criminal trespass; denial of entry; permission to enter; exceptions
Sec. 2. (a) A person who:
(1) not having a contractual interest in the property, knowingly or intentionally enters the real property of another person after having been denied entry by the other person or that person's agent;
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(b) A person has been denied entry under subdivision (a)(1) of this section when the person has been denied entry by means of:
(1) personal communication, oral or written;
(2) posting or exhibiting a notice at the main entrance in a manner that is either prescribed by law or likely to come to the attention of the public; or