noun, noun or participle which takes 'suru'
sign on; log in
Computing term for logging into a system or service. Often used as a noun or with する.
システムにサインオンするにはパスワードが必要です。
You need a password to sign on to the system.
ログイン is the more common general term for logging in; サインオン is used in specific computing contexts, sometimes implying a session start.
サインイン is a synonym often used interchangeably, though サインオン may emphasize connecting to a network or service.
Variant with interpunct; less common in running text.
Borrowed from English 'sign on', used in computing contexts.