1. To enter one's or someone else's name or signature onto a ledger in order to be admitted into some place or event. A noun or pronoun can be used between "sign" and "into." Everyone has to sign into the event so no one can slip through without paying. Please sign your child into playgroup at the start of each session. You should sign yourself into a hospital if that pain doesn't ease up.
2. To enter into a computer, website, or computer program by entering in the required personal information, such as a password and username. I can sign into the computer at the library and email you the files from there. You will have to sign into the website before you can complete your purchase.
3. To ratify a piece of legislation by putting one's signature onto it. A noun or pronoun can be used between "sign" and "into"; almost always followed by the word "law." The president has refused to sign into law and bill that does not include funding for her controversial infrastructure plan. The governor has already indicated that he will sign the bill into law if it passes through the state senate.
See also: sign
1. To ratify some legislation by affixing a signature, seal, or other mark, so as to bring it into some state of existence: The president signed the bill into law.
2. To provide the necessary information to a computer for someone to be allowed access to some set of computer resources: I'll sign you into the website so you can read the whole article. I signed into my account on the website and checked my order status.
See also: sign