Hi, as you mentioned it is leather, the pattern is from a process called boarding, which can be used to give a finish that can look like other exotic skins or just decorative patterns. I believe this is the latter. I might call it a bark effect.
The Tony Lama boots I had were size marked in red, quite a large number quite far down inside. I believe they are marked before they are completed, so it's not at the top as you may expect.