My flying school made us all wear Uniform and Rank Slides, even before we had seen the inside of a small a/c.
To start with
Blue pilot shirt and a plain (nothing on it all, just plain navy blue) slide
The first time you take off and land an a/c without help
Blue pilot shirt and a thin silver bar
First solo
Blue shirt, thick bar
on gaining NPPL
Blue shirt - 1 thick and 1 thin silver bar
On gaining JAR PPL
Blue shirt - 2 silver bars
On gaining Night Rating
Blue shirt - 2 gold bars
On gaining Instrument Rating, you were considered not to be a PPL, but training for a CPL, even if you never wanted it, so you had to change your shirt for a green one - and try getting a green pilot shirt anywhere except their shop. You also had to get green slides with the 2 gold bars.
The slides also had other markings toward the top. A Maltese cross (nicked from St Johns Ambulance) if you were a First Aider, and laurels for instructors.