In the very early days of Windows 95, the distribution servers were not particularly powerful. The load of having the entire team installing the most recent build when it came out put undue strain on the server. The solution (until better hardware could be obtained) was to have a stack of floppy disks in the office of the "build shepherd". (The job of "Build Shepherd" was to perform the initial diagnosis of problems with the build itself or with verification testing and make sure the right developer is called in to address the problem.)
If you wanted to install the latest build, you had to go to the Build Shepherd's office and take one of the specially-marked floppy disks. When you finished installing, you returned the disk.
In other words, the floppy disk acted as a real-world semaphore token.