1
general::
Record the departure of a person or the removal of an object, as in He turned in his room key and signed out about an hour ago, or I asked the librarian how many books I could sign out. [c. 1930]
American Heritage Idioms
2
general::
Phrase(s): sign out
to indicate that one is leaving a place or going out temporarily by signing a piece of paper or a list. • I forgot to sign out when I left. • Please sign out every time you leave.
McGrawhill's American Idioms And Phrasal Verbs