Symbols help unite groups. Online or offline, we share the same symbols as the groups we belong to.
Symbols is any idea, image, expression, or entity which has a unique meaning to insiders. Outsiders might not understand it, but insiders do.
The quantity and depth of connection with the symbol, the more we participate.
But it's hard to introduce new symbols. It feels fake.
This is why hashtags like #pepsitothemaxi never take off on twitter.
You need to identify existing, unknown, symbols and amplify them to a broader group. This works both online and offline.
In the 1940s, Shmaryahu Gutman turned Masada from an unknown story of suicidal extremism to a powerful symbol for Zionism (and a popular tourist attraction).
Element14 is quite literally a symbol for engineers.
Many old-timers in the community space share chat moderation and usenet groups as symbols. They might even share some classic books as symbols.
On Mumsnet, the expression penis beaker has become a symbol.
If your community lacks clear symbols, look for existing interesting stories, images, or other idea that merits greater recognition.
Begin referencing it subtly in content and discussions. Interview someone involved with it. Use repetition over a sustained period of time to increase awareness of the symbol. Bring in early adopters of the symbol to mention it more frequently.
Once established, reference the symbol liberally within the community. Reinforce your community's symbols throughout the site.