old school tie

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A necktie that has the colors of a British public school.
• noun The upper-middle-class solidarity and system of mutual assistance attributed to alumni of British public schools.
• noun The narrow clannish attitudes characteristic of the members of a clique.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun necktie indicating the school the wearer attended