Over 100 platforms to choos from now..
This is a mounting platform and sign bracket for the F-16XL Kit Card kit card by phabulousphantom available at https://www.printables.com/model/189092.
These parts are designed to attach to a 3UDC pivot arm so that you can present this model anyplace you have a 3UDC socket.
You can find the Kit Card Tree library of mounting hardware and instructions at https://www.printables.com/prints/126495
Thanks to phabulousphantom for sharing this print.
The author remixed this model.