I haven't seen anybody asking this. I just went to check some statistics about the Retrocomputing site and one of them featured a cloud of StackExchange sites, each one with its logo with a size relative to the size of the community. Of course, RC is still small, and it currently wears the default speech ballon logo.
So is there a defined procedure to design/propose a logo for the site? Has the site to reach a specific size? How does all this work?