What does the floating green shovel mean?

These are alliance flags or bookmarks, your R4/5 can place them on a map to show the team where to go or what to do. They can also place a timer on them, or a label to explain why they're there. (Unfortunately these don't translate).

There are 6 options/colours, and each alliance will use them differently. The green flag is one of these, as is the pink bomb, red knives, etc.