Jefi,
During show press Ctrl+P to show the pen, Ctrl+A to shows the arrow again,
Ctrl+M to show or hide the ink you applied.
Be aware that you will get a very small dot, easy to miss.
An alternative would be to use the pop-up toolbar at the bottom left of your
screen, you can click on the second button and choose between pen, marker
and such. If the toolbar does not pop up, go to Tools - options - on the
view tab check show pop-up toolbar.