How can I copy all my custom icons from one computer to another? Currently, when I open a project synced to dropbox onto another machine, the icons do not sync.
Is there a way to sync them automatically along with a project file?
Thanks. 
While it addresses more than just icons, the knowledge base article on migrating settings to a new machine, specifically the Transferring Scrivener’s Preferences section, will help you find where they are.
As for syncing these settings, it’s doable with symbolic linking. You have to use workarounds with Dropbox, because it doesn’t let you pick and choose what to sync from wherever it currently sits.