Whats the deal with the numbers or whatever on the lower heel section of the shoe
Vionic Awaken Wide Fit Ankle Strap Sandals
£125
Vionic Mar Ankle Strap Sandals
£130
Sneakers KURT GEIGER Lettie 8487200309 Black | Vionic Delano Platform Sandals
Vionic Alondra Platform Sandals
Vionic Chardonnay Heeled Leather Sandals
£140
Vionic Brown Miramar Slides
£120
Vionic Rejuvenate Slides
£85
Vionic Val Tumbled Leather Slides
£70
Sneakers KURT GEIGER Lettie 8487200309 Black | Vionic Rejuvenate Slides
Vionic Bella Sandals
£75
Vionic Rosabel Heeled Sandals
Vionic Marina Ankle Strap Wedge Sandals