If you don't sign, you can hardly use third-party software. It is said that it is for security reasons, that is, Nokia is not responsible for the security of third-party software. If you want to install third-party software, you must be responsible for the bad consequences it causes. Therefore, you are required to sign.
Self-signing is the same as signing, which means you need to sign the software yourself. Signed is signed by a software development company and can be installed directly.
It is recommended to download the software recommended by the set-top box sticker. The safer method is to use the online detection in the upper right corner after downloading.