Obviously when leaving items, discretion is a MUST. To the person placing the questionable item, their intentions may be good, but at the same time, common sense must come into play.
Several months ago, I was out caching off of Hwy 88 (Arizona), and found 2 WWII era weapons clips with 5 LIVE rounds of rifle ammunition in each. Keep in mind, these rounds were manufactured over 50 years ago, adding to the "Oh My God" reaction when I found these in the cache. I took both out of the caches, without leaving an item because I felt this to be entirely unsafe. Who would be to blame if one of those rounds fell and fired, killing someone?