Can't edit a layer with a little square icon at the bottom right

[EllenH42]

I need to edit one layer of a file that I created six years ago and I can't find any way to do that. It was for something I have never done again since then.

Four of the layers, one of them being the one I need to edit, show a little icon on the layer in the sidebar. The layer is not editable.

It's a square which has, at each of the four angles, another very tiny square. I don't remember what I did at that time and have no idea what this icon means.

 

Can anyone help?

[Semaphoric · Accepted solution]

That is a Shape layer. Select a vector tool, like the Path Selection tool, and look at the Properties panel.

[EllenH42]

Thank you. The text was converted to shapes for some reason I can't remember. I think I know what I have to do now to change just one line of text.

Your reply was very helpful to me even if it seems absolutely obvious to you!

[Semaphoric]

A Smart Obejct has a different icon: