That's the way I used to do it at my previous company in plain AutoCAD and in a competitor's application. We used hexes as a 'line ref symbol' with the sheet number above the line number. In AE, I think you can config to use the hex references, and then modify the particular symbols used to remove the hex if the hex is undesired. That should give you the configuration you are wanting, sheet number centered above line numbers.
- Jay
P.S. Duh... after looking at the sample drawing, I see you are wanting to use the hex references. When you create a signal reference, the dialog box will give you the option of selecting from several styles. One of the styles looks exactly like you have in your sample drawing.
