When your desk has a board at the back, your screen is as flat at the back as at the front, or your office is split into sections by dividers - why not mount your own signs, cards and whatever using a holder made from waste cardboard? Here I have made one to fit the back board on my desk, so I can mount my cardboard biker picture.
Step 1: Cutting
As you can see, a simple cardboard rectangle is all that is required, large enough to be bent into a U shape that will fit the size of the board on which you want to mount it. The two large slots shown here are to mount the holder onto the board, while the smaller ones are sized to mount my cardboard picture.
A sharp craft knife is better for cutting corrugated cardboard than a pair of scissors, which tends to crush the edges. Measure the thickness of the board to determine the width of the slots, and make the slots deep enough to be steady when in use. I mark out the slots using a pencil and some kind of straight edge. For the cutting it is OK to do it by hand, working away from the corners, but avoid rushing. Remember that you have to cut through the corrugations, and these can push the knife off course.
Don't worry if it goes wrong, there is always more cardboard!
Step 2: Installing and Onwards
Here is the holder on the back board of my desk, waiting for me to fit my picture.
I also used this one to mount a large cardboard Christmas tree, and others to hold a small shelf, books, fluffy toys, whatever I want to store off the desk top without losing it forever in the depths of my drawers.
Make sure not to use them near a source of heat, such as above the ventilation slots of a screen, as no one wants a fire.