You may know that you can paste icons onto documents and groups in DEVONthink to easier distinguish them: copy any picture, then open the Info panel for the document or group (Tools > Show Info), select the icon, and paste your picture. What you may not know is that you can do the same with DEVONthink databases in nearly the same fashion. Copy the icon you would like to use to the clipboard, then select the database package in the Finder, open the Info panel (File > Get Info), select the icon field, and paste your picture.
See the screenshot to the right, posted by power user Mark Grimes. Thank you, Mark, for this wonderful tip!