sign for someone
to sign something, using one's own signature in place of someone else's signature; to sign something, using another person's name, adding the phrase "by [one's own name]." He's not here. I will sign for him. Where do I sign? Who will sign for Mr. Wilson?
sign for something
to sign a piece of paper indicating that one has received something. Would you sign for this, please? Ted signed for the package and opened it up.
sign something for someone
1. to sign one's signature on a paper in place of someone else's signature. Would you please sign this for me? I can't sign it right now. Would you sign it for me?
2. to sign a paper for another person, using that person's name, adding the phrase "by [one's own name]." When the delivery comes, will you please sign my name for me? I signed Ted's name for him.