Neil, would this help?
Manage > Admin Control Panel > Settings > Graemlins
A Graemlin is our special term for emoticons (named after the member who first suggested it 15 years ago). In this section, you can control which standard Graemlins are available for your community, and create your own custom Graemlins. Just click “add Graemlin,” choose a keystroke, and upload your image. Note that while most Graemlins are tiny, this feature does allow you to upload large images that can then be accessed via a short keystroke. If you wish, you could upload your logo as a Graemlin and use the keystroke :logo: to make it easier to insert it into forum content.