These are more suitable and descriptive that the circle ones. We might want to fine tune and tweak them a bit, but it can be done when we actually implement it.
I had initially thought about clicking and viewing the comments, hence I placed the icons with other properties. In addition to this there can also be a menu entry in Layer menu - Layer > Show comments which will show hide these icons on the layer. So that users can turn off seeing comments icon and make it less distracting when not required. It will be preferable to save the state of the menu with the document. So that when sending files I will enable the comments to show and the user receiving the file can see them hen opening the file. After checking the comments he can switch off the visibility and do his work.
On another note a disadvantage of keeping the icons on the left side like in your mock is that it will be too close to the layer type icon which itself is small and this would lead to slight clutter near the name of the layer, it also pushes the layer names a bit which might be an issue when there are nested layers and the layer name gets truncated further.
Yes I like that too, But your comment icons seems more apt to me.
I thought about keeping the group to green and layer/mask to orange but these were arbitrary colours I came up with they can be something else which go well with the various themes of Krita. We can leave the colours aside as they are not necessary once we use your comment icons.