I use a pen which you can wipe off with ethyl alcohol. This works well for a couple of hours but not completely after one day. You may draw the lines on masking tape, on the backside or make only little points which you can also wipe away with acetone or MEK when you prepare the surfaces to be glued. Try to use straight lines because they are easier to tape and it's less likely that MEK runs under the edges of the tape.