When Mrs pj moved to my house, several boxes had stuff in plastic bags (like yarn). Anything that had something tender at the top was clearly marked "NO KNIFE" at the top. We had a plastic knife for opening said boxes. It had a long, wide piece of ribbon tied to the handle so we could find it more easily. (Copier paper boxes eliminate this problem since the lids lift off rather than tape shut.)

I mark heavy boxes with a big red "H" in a circle on all four sides plus the top.

I mark fragile boxes with a big red "F" in a circle on all four sides plus the top.

In moving Mrs pj here, and moving my mother five times in her last years, absolutely nothing got broken. When I moved from DC to here, one glass broke. It was in a box my housemate packed by pouring a layer of styronuts in the bottom of the box, putting in the glasses, and pouring a layer of styronuts on top. When I pack anything fragile, each item is individually wrapped in paper.