>>13625It doesn't have to be a flag, just make it a funny symbol associated with the board.
For example, Wojak for /r9k/, Reddit alien for /pol/, 404 or desu girl for /a/, Bane for /tv/, Stirner for /lit/, RX-78-2 for /m/, Karen for /int/, that angry guy that represents /v/ in 4chan webcomics for /v/, Bridget for /lgbt/, Zyzz for /fit/, Willy for /his/, etc. I'm sure the mods could come up with better stuff than I can.
Or alternatively, just go for the boring route and only have the name of the board included, no memes.