Here is a great way to share design element notes between multiple users of a single design. (Or reminder notes for a single user)

Begin by selecting the ‘Notes Tool (N)’ on the Toolbar, as I have captured below.

Share Notes in Designs with multi-user layouts.

With the ‘Notes Tool (N)’ active and your design document open, resize the document window so that there is excess room around it as I have captured below.
Then click anywhere in the excess area (dark gray) to add an empty Note.

Share Notes in Designs with multi-user layouts.

At the insertion point, inside the Note, type the required instruction that you would like preserved with the final document.

Share Notes in Designs with multi-user layouts.

To modify the ‘Author’, Font type and Note caption color, go up to the Options Bar and adjust the Notes’ preferences.

Share Notes in Designs with multi-user layouts.

Double click on the icon to collapse it from view.
Double click it again to expand it into view.

Share Notes in Designs with multi-user layouts.

Add multiple Notes with varying Options Bar properties such as Color Codes as I have captured below.
Note: The Active Note is the indicated with a hollow color while the inactive ones have a solid color fill.

Share Notes in Designs with multi-user layouts.