Around the side of those stickers we've used an arrow so as not to mark up the wrong side of the tape. With that done I've taken an off-cut of 1" tube and marked out the width of the joint, using the same straight-edge to mark an 'X' for the centre-punch.
I may be teaching granny to suck eggs here, but of you want to be super-accurate you can drill from both sides in the absence of a power-pillar drill, which I've given away. I trust to my own judgement and go in from the top with 4mm pilot-hole. This usually results in an off-centre hole on the other side of the tube, but then I go in from the backside with the 6mm drill-bit (that matches our hex bolts) so that I can lean on in the hand-drill in the required direction to centre things up.
