Stamps notes can be deleted using the Comments catalogue which will also remove them from the document.

Alternatively:

  1. Select the Hand tool (Hand tool icon) on the main toolbar
    or the Stamp tool (Stamp tool icon) on the Commenting toolbar (View->Toolbars->Commenting)
  2. Click on the stamp of the shape to be deleted.
  3. Press Backspace or Delete on the keyboard
    or right-click on the outline and choose Delete.