There are two settings you can set to influence the "separator character" that gets used in places in the app -- they are "Separator character in navigation bar" and "Separator character in the user navigation bar" and they are both in the Display > Front Page.
There are some skins that hide the separator characters set in the admin and replace them with a skin image -- you should use a developer tool (like firebug) to see if this is the case, and if it is, you should see some css that shows a skin image (or another image) being used. If this is the case, you should be able to change the image via the "Community Style" tab in Lithium Studio.
