Having been at school in England a very, very long time ago, we used to use these marks in all of our maths work involving money. The " was written between £ s and d., as I recall. I think I used to write it slightly raised up from the bottom of the line, but perhaps it should have been on the line and I was just a bit sloppy with my work! I believe they were simple separators, used to ensure there was no confusion as to which number referred to £s and which to shillings etc. and were particularly valuable as column separators when performing additions and other calculations.