Remus was stationed up near the Astronomy tower. He wasn't exactly proud of what they were doing, but he had to admit that there was a sense of brilliance behind it. Not to mention it was for James' birthday, so there was no way he was going to skip out on it. They were the Marauders, after all. He would've liked to have been stationed closer to the others, if only to help keep them out of trouble. Hopefully this would all go according to plan, though.
He felt the stone grow warm in his palm and knew that meant that James was signifying it was time to go. Remus looked around, to see if anyone was nearby. Still alone, he pulled out his wand and cast the charm James had indicated they needed to use in order to carry out the prank. Once it was done, he tucked his wand away and started to make his way back to the Great Hall to meet up with the others and await to see what sort of ruckus would arise as a result of their brilliance.