NOTE: This information is not provided as legal advice. Always consult a lawyer and seek legal guidance.
Iowa code 702
Here is Iowa Code 702 regarding dangerous weapons.
702.7 DANGEROUS WEAPON.
A “dangerous weapon” is any instrument or device designed primarily for use in inflicting death or injury upon a human being or animal, and which is capable of inflicting death upon a human being when used in the manner for which it was designed, except a bow and arrow when possessed and used for hunting or any other lawful purpose. Additionally, any instrument or device of any sort whatsoever which is actually used in such a manner as to indicate that the defendant intends to inflict death or serious injury upon the other, and which, when so used, is capable of inflicting death upon a human being, is a dangerous weapon. Dangerous weapons include but are not limited to any offensive weapon, pistol, revolver, or other firearm, dagger, razor, stiletto, switchblade knife, knife having a blade exceeding five inches in length, or any portable device or weapon directing an electric current, impulse, wave, or beam that produces a high-voltage pulse designed to immobilize a person.
I am a bit surprised that there is no mention of billys, clubs, batons or any other bludgeon in this law. The way the law is written I am sure that they are included within their “dangerous weapons” category. I did some searching for additional information on bludgeons in Iowa and did not find any concrete answers.
Normally on your properly you can carry as you wish, but I would be careful of partially concealing a baton. I am sure it would be considered concealed if your shirt covers the top half of the baton.
I would suggest contacting an attorney to get a solid answer on this. I would go on the side of caution and not partially conceal the weapon just to limit your chance of spending a few nights in jail. As I am sure you know, not all officers know every aspect of the law especially when it comes to telescopic batons, expandable batons and bludgeons.