What do the small labels on the designs in the Designs column mean?

The number is the design's place in the book. "AI" or "Photo" marks a page made from a picture. A lock means the design is locked. A yellow mark means the design needs a new drawing (hover it to read why). A page not drawn yet shows a spinner while it is being made, "AI page: no idea yet" or "(idea): not drawn yet" for AI pages.