The devs recently admitted they are working on adding paper to the game, so that would be a nice way to attach 'post-it-notes' to a container.
I think the convenience of seeing the notes on mouse-over of a container is well worth it and doesn't present much of a security risk, if people are rummaging through your containers already they are going to find what they want fairly quickly with or without clues. Heck if your smart you could even try to trick them by labeling your treasure chest 'dirt and branches and other worthless stuff' no one would ever look in that
