I haven’t know anything about Steampunk until today, but it’s a subculture of people who have a really distinctive clothing & aesthetic style. Steampunk is the fashion of the Victorian steam era as it might have developed had the era lasted longer. So it’s got elements of today & the future based on steam power and other technologies of the Victorians.
It’s really cool, and generally not as heavy and dark as the Gothic niche. There are some great picture of the clothing style at http://www.lacarmina.com and I’ve also embedded a video of a Steampunk band just below too.
If you’re selling Steampunk jewellery, mannequin jewellery stands would probably be the way to go.