Depending on the presence and amount of content in a note, the outline view (and views with the same icon) will show a slightly different icon (and in Attribute Browser, chart and Timeline views).
- No note text. A simple half-height rectangle.
- Zero to 7 characters. A vertical rectangle with no horizontal bar inside.
- More than 7 characters. A vertical rectangle with a single horizontal bar inside.
- More than about 60 characters. A vertical rectangle with two horizontal bars inside.
- More than about 500 characters. A vertical rectangle with three horizontal bars inside.
- More than about 4080 characters of text. A a vertical rectangle with four horizontal bars inside.
In Map view (and views with the same icon), the presence of note content is shown by a 'dog-ear' icon on the note; the above granularity of content is not represented.
Agent icons are similar except the thick bar is at the bottom, not the top. Disabled agent ('frozen' via $AgentPriority) have an empty bar at the bottom of the icon.
The varying agent/note icon is not immediately obvious to the eye in Outline view, but once you realise it is there the difference it becomes more intuitive as a way to tell apart Notes and Agents. Maps have a different, but similar, visual layout to differentiate note vs. agent containers.
The fill colour of the icon, indicates the age of its content.
Prototype notes also show a light green coloured circle behind the icon (here darkened slightly from default value for better contrast). The colour used is set in the Map Preferences.