An Interesting Design Problem

A customer looked at the toe saver product that ScopeRoller sells, and wants something like that to allow him to quickly mount signs to a mounting plate.  Right now he uses bolts to do so, and screwing in a hundred plus bolts is very time consuming.  The toe saver product is fast, but this needs to be something that locks the sign to the mounting plate pretty rigidly.  My thought is that perhaps a stud on the back of the sign goes through the mount plate, then something that slides over the stud and locks into position.  I suppose that I could make a stud where I machine a notch in it, and whatever slides over the stud locks into that notch.  Any ideas what this gadget is that would slide over the stud and lock into place would be called?

Problem solved: a 1/2" long sleeve that screws into a hole on the mounting plate; a hole through the sleeve and the stud from the sign; a detent pin that slides through the sleeve and the stud.  By turning the sleeve into the mounting plate, you adjust how tightly the detent pin holds the stud in position.  The detent pins are less than $2 each (maybe a lot less in quantity); the sleeve and stud are off the shelf items that require no machining.

UPDATE: Does anyone make a hollow version of a male-female standoff?  Something threaded to screw into a hole, but hollow inside the threaded portion?