Could you add the ability to customise the icon which is shown for each document both within Grist and in the browser toolbar (favicon)?
This would help users to feel more comfortable using Grist for their projects and also make it easier to identify the document at a glance. It would also help to differentiate between documents when having more than one open at a time (multiple browser tabs).
Another creator (coincidentally, also named Chris ) had a similar feature request for page names. Feature Request In this thread, super123 suggested using emojis. I just tested it for page names and it helps.
Not a favicon but it can help you identify documents at a glance.