1) FOOT WIDTH SYMBOL: there are two footbed widths--Narrow and Regular. Regular width symbol is an open footprint and the Narrow width symbol is a filled-in footprint.
2) BIRKENSTOCK SIZE: the big number is the Birkenstock size. The above footbed shows a Size 38 (left) and Size 43 (right).
3) GENUINE LEATHER SYMBOL: indicates liner is made from genuine suede leather.
How to Understand and Read Size/Width of Birkenstock footbed