Symbols for "All level [x] rows"
 

When I open the Utilities drawer, I see listings for "All level 1 rows", "All level 2 rows", and so on until "All level 10 rows".

To the left of each "All level ..." is a square icon. Some are squares with a Capital "A" in them, some are empty squares formed by dashes, and one is a square with a blue checkerboard in it. Why do some of these have different looking icons? What do they actually represent?

Do a search for style chits in OmniOutliner's help:

[B]Style chits[/B]

Style chits are the small squares that appear in the styles palette, styles view, and the Style Attributes inspector. They visually approximate the style they represent. If the style cannot be expressed within the chit, it will take on a default checkerboard pattern.

A chit can be dragged onto other chits or onto a selection in the outline. Normally this will copy the chit's attributes to wherever you drop it.

Dragging the chit for a named style, however, applies the named style itself as a single style attribute, which changes along with the original named style. If you hold Command while dropping a chit, its style replaces any existing styles on the text.

Chits in the styles palette and in styles view can be edited by clicking them and then using the Appearance or Row inspector. While a chit is selected, all of the rows it affects will be highlighted.

So those using an A indicate the non-default font being used for that level; the empty squares formed by dashes represent levels with all default settings; the checkerboard indicates levels with more than one non-default style applied (which can't be represented easily by a character or colour).