My wife likes Victorian things, and we found these awesome faux-Victorian iron shelf brackets in a shop a while back. I needed to make some small shelves for the same area of the living room so I decided to make some smaller brackets in the same style. I found a similar shape online (using the google search "wrought iron shelf brackets victorian"), and used Photoshop/Inkscape to turn the decorative scroll work into a vector file I could import into Tinkercad. Then just added the brackets, and screw holes and done.
The intent is to mount them with screw holes to the inside, so I added a slight V groove to the edge to make it look slightly inset. This puts the matte bottom surface facing out, which I think works.
The board I will be using will 4" pine board (which comes out to less than 4 so I made these around 3 1/2".
I modified the the ends of brackets to make them slightly shorter and rounded them a little. These fit the boards a little better and look nicer. These are marked v3.
Printing note: The brackets are symmetrical so you really don't need to print both L and R brackets.