It shall be lawful to use any device which
(1) is operated by the explosion of small amounts of gunpowder or other explosives,
(2) is designed to discharge poison into the mouth of a wolf, coyote, fox, wildcat or other predatory animals upon the grabbing or seizing of the bait attached to such device by such predatory animals,
(3) does not discharge any ball, slug, shot or other missile, and
(4) does not endanger the life and limb of any human being or animal, other than a predatory animal, during the legal trapping season for fur-bearing animals; PROVIDED, such device may be used at any time by any agency of the Game and Parks Commission or of the federal government or by persons having the written permission of the Game and Parks Commission. Such lawful device when used shall be set not less than two hundred yards from any federal, state or approved county highway and not less than one thousand yards from any rural school, while functioning, or any inhabited dwelling without written permission of the resident of said building; nor may such device be used on the land without the written permission of the owner or operator; PROVIDED, that it shall be unlawful to use any such above-described devices unless the user shall, in addition to the other requirements of this section, post the land upon which the devices are emplaced with signs at least eighteen inches square and with block letters at least two inches in height and displaying the words DANGER, CYANIDE GUNS IN USE or with the official signs furnished for such a purpose by the United States Fish and Wildlife Service. Such signs shall be placed at all entrances to the area where such devices are set and a post shall be set by each such device displaying at least two of the above-mentioned signs in a manner so that such signs are plainly legible from all directions.