Hello! Great question! For this jam, using real-world Sign Languages is preferred, as the main goal is to promote Sign Language inclusion in games for D/deaf and signing communities.
However, if you would like to create your own Sign Language, you can, but try to also include a real-world Sign Language. For example, this could be done by showing translations into ASL, or featuring a character who is bilingual in both your Sign Language and real-world Sign Languages.
From the 14th of June, I will be hosting the "Not My Lang" game jam, where constructed languages including Sign Languages are welcome. So you'd also be able to submit a game there using a Sign Language you've made.
Thank you again for asking, and best of luck with your project! 😊