It seems the normal thing from visiting a few art shops to put a signature in the bottom right hand signature. But what about other information - does this go on the back? A title, a date (not sure that'd be just year, month/year) - do paintings scribble this on the back in ink, pencil or in the paint they've painted in. Perhaps more established artists have 'paperwork' with their paintings. And perhaps beginners do the former. Maybe it was different historically... I can imagine painters a few hundred years putting the info on the back perhaps just in case the painting got lost from its owner/painter.
Having said that, I bought a sketch in a charity shop as I wanted the frame. I actually quite like the sketch too (v v simple line drawing of a barn) and it would be nice if something had been written on the back about it.
Not the same thing I know but on a quilt, which is often just a piece of art in fabric if you are showing them, you put a label on the back. It includes your name, date of completion, who it is for and the name of the quilt if you have one. At shows they are often displayed with a brief story of how they came to be, motivation, inspiration and that sort of thing.
I would think that you can put what you like on the back of a painting but I assume the same info would be useful. As to what you do it with (paint, pen, pencil etc) surely that depends on what you have drawn/painted on? I would have thought that pencil would be fine for most things as it wouldn't show through on the front.
Hopefully somebody who uses other media will be along shortly.
I would have thought (and that is a guess - somebody who went to art college would surely know better) that that kind of info would have been pencilled/inked/painted on the bank as a way of keeping record as much as anything.