I think those used to be the old air drop blocks, or /gimmie blocks back in the really early pre alpha stages.
Some sort of admin tool block used to help players that may have had misfortune, most commonly with players using hacked clients and destroying other players bases with it.
I think it's a block that's supposed to randomly change into ammopile/trash/backpack/other type of loot container on generation of the chunk, but somehow glitched out.
I took this block back to my base and placed it on my claim block just for fun. I then started noticing a dramatic increase in loot bags dropped from zombies in close proximity. I did not research any loot perks.