The only times I have ever seen it done OFFICIALLY were either by autopen which contained an original signature and was then marked with the autopen # or with an annotation that stated “By Direction” with the note on who was signing by direction.
The reasons for this are that you need to be able to trace who actually applied with the wet ink or autopen signature so that if a question were to arise it could be traced.
I’ve never seen an aide sign in any other manner for official correspondence.
I agree. It just seems so appropriate that NanTheSanFranGran would have some peon do it for her. She is much too important for such menial tasks.