Don't use user-bookmarks-symbolic icon
- Ubuntu 18.10
- Yaru theme (its icons are derived from the Suru icon theme)
With Adwaita, "configured" partitions have a star icon. In Ubuntu 18.10, it shows up like this:
I think that's a reasonable icon to represent "user-bookmarks-symbolic". If that's not what you intend, I suggest you switch to
starred-symbolic (looks the same as Adwaita) or
dialog-information-symbolic (lightbulb in Adwaita; black "i" enclosed in a white circle for Yaru).