Help identifying unusual rank slides

Hey, Navy over here so if the answer is mega obvious excuse me lol, just me being curious

Saw a RAF officer today in working rig, believe his rank slides were Squadron Leader (LtCdr equivalent), but he had what looked like wings at the top of the rank slides? Whole rank slide was blue with gold wings at the top.

Never seen this before, any idea what it could be or is this guy just cutting about in custom rank slides?