They call themselves "stackers". It's not just bars; companies sell "rounds", which are coin shaped designs of .999 silver, gold and other metals. Silver is probably the most popular though, as most stackers are certain that its present $20 or so price per ounce is far lower than it should be.
The rounds and bars can be quite artistic. They can also be campy and quirky:
But wait, there's more: some of these stackers like to pour their own PM (Precious Metal) bars. It's probably mostly a guy thing: there's very hot fire, destruction (melting whatever you are using, other bars, coins, battery cable lugs) and there can be creativity in the molds. An element of danger adds to the allure, I'm sure.
Things don't always turn out well. At Test run silver bar a stacker described the result of his first attempt as a "silver turd". He promised a video of the process, but his wife and daughter nixed that idea.
Peruse the wide variety of PM products at this link (no, I get no commission or anything else for sending you there).