It would be great if there could be an icon that shows next to tasks/subtasks in multiple lists, rather than you having to hover to see this information.

Sometimes a Task/Subtask can seem out-of-place/confusing (e.g., because of a naming convention), and it's not clear until you hover and realise it's because it is also in another list.

So a simple icon in the "Task Properties" area would really help - i.e., next to the Task Description, Subtasks, Dependencies, and Tags icons.