For centuries, architects added "picture rails" around the periphery of rooms to allow for easy, rearrangeable, and damage-free picture hanging. I guess they're not in style like they used to be, but my old building has them.
When I realized that's what the weird mid-wall molding was I thought I should use it for its intended purpose—hanging pictures! However, the commercial hardware for this is expensive and/or tacky. I had a better idea.
The picture rail is just a piece of molding about 8' off the ground. If you want to hang something on it, you simply need to make an appropriately shaped hook. I took 1/4" square × 3' aluminum bars (~$3 apiece from McMaster) and bent the ends in a vise so they'd grab on:
Then I did some looking, and found that a standard "medium" size binder clip (or what Staples calls medium, 1-1/4" wide with 5/8" capacity) can be cajoled to fit around the rod. You can easily adjust the position of the binder clip by rotating so the binder wing is perpendicular to the rod, and it will freely slide. Then just push down to lock it and grab on, as it is in the photos. Here's another one from the middle of the bar:
Then it's just a question of arranging pictures as you like. It's pretty easy to slide the clips up and down, though it's best to remove the picture it's holding first. And it's very easy to change the position of a whole column...just pick the whole thing up and put it anywhere on the picture rail you want!
Pretty easy, pretty cheap, and pretty satisfying outcome. ⁂
In case you're wondering where I got the pictures: there's this very neat collection at the Mid-Manhattan branch of the New York Public Library, called (simply) the Picture Collection. (N.b. this is not at the Main Branch, but across the street from it.) Most of the collection circulates, so if you have a library card, you can take out up to 30 images at a time, which they give to you in one of these neat envelopes:
It is definitely worth checking out if you're in the area. They have millions of images, sorted by subject. (I borrowed one from every letter of the alphabet: astronomy, beard, Congo, dance, electronics, flood...) You don't need a library card to browse through them, just to borrow.
Without the pictures, the hangers make a very spare modernist sort of sculpture—or a blank canvas for some interesting next wall-mount project of yours.