Map comments are objects used by editors to annotate the Waze map. They are used as notes, explanations, warnings or reminders for editors and can be made by any editor anywhere, regardless of editable area. They appear as white points and polygons in the Waze Map Editor.
Hover your cursor over the 
icon in the header bar and select the area or point option.
It is recommended to fill in the expiration date.
See also the USA wiki