I tilt the same framed photo every time I visit my parents

For almost a year, I have rotated one framed hallway photo a few degrees whenever I visit my parents. My dad notices within minutes, straigthens it, and complains that the hook must be loose.

The hook is perfectly fine. Last month he replced it anyway, so now I feel slightly guilty. I should stop, but watching him inspect the wall with increasing confusion has become part of every visit. He still has no idea it is me.