Guide indicators in ruler don't show when the guide is first created but do show when guide is released and then moved again, see steps below to reproduce the issue. (reported here by TomHu)
Select the Move tool
Drag a guide out and as you will see no indicator in the ruler
Release the guide
Now move that same guide again, the guide now extends into the ruler area.
I'd say this isn't by design, but a bug.
Another point, when dragging a guide out initially, th