Book seven. Probably. Because I'm making the assumption that Lily and James're buried, or at least have a monument after them, in Godric's Hollow. As Harry plans to go there, I believe that he'll make a stop to say hi.
It seems my art post are somewhat sporadic. But as wonder never cease to exist, here's one anyway.
This is the first one in a series of pictures from the time when the marauders attended Hogwarts. One of them has taken a camera with them and Moony feels the need to make a note at the bottom. Sirius can (of course) not let this be.