This is a mounting platform and sign bracket for the Fokker DRI kit card by Toto_28 available at https://www.prusaprinters.org/prints/99137
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.prusaprinters.org/prints/126495
Thanks to Toto_28 for sharing this print.
The author remixed this model.