In 1961 artist Piero Manzoni preserved his excrement in 90 signed cans, each containing 30 grams of his solid waste. The "Merda d'Artista" are becoming more valuable over time.
Via Oddity Central:
In 2007, the Tate art gallery in London, bought one of Manzoni's 90 cans for £22,350 ($30,000), and while that may seem like a lot for what is literally just canned crap, they actually got a great deal. In 2007, another can of "Merda d'Artista" was auctioned off in Milan, for a whopping £81,000 ($108,000). Crazy, right? Not really, just another good deal, because Manzoni's cans of poop are currently worth around $300,000 apiece. Last year, someone bought can no. 54 for £182,500 ($242,000).