Universal Full / Empty Flag for Trash Can / Recycle Bin / Waste Bin

This model fits on the handle of the can.  There is no glue required and no supports are necessary during printing.  Printing the part as shown with PETG will allow the part to flex and fit around the handle without breaking.  Set the vertical wall perimeter to 10 to make sure the part will be filled in a direction to support the flexing.  The FreeCAD parametric model is included if there is need to change the flag length or handle diameter (32mm default).

After putting the trash can on the curb, flip the flag up and push it near the support so the pin will rest against it.  When the can is emptied, the flag will fall down. 

Another model is similar that requires support and is more specific to a can that has a septum support on the handle: Full / Empty Flag for Trash Can / Recycle Bin / Waste Bin by Teraflop | Download free STL model | Printables.com