something he saw on her foot..

Just over half way, when our couple were in the flat.. he saw something that looked for all the world like a tattoo on her foot (He saw it because she had no stockings and (presumably) small, poor shoes on. It disconcerted him..
What was it?
Or was it just she had poor shoes.. which is why buying her better ones was so important?
But I'm sure there was something on the exposed part of her foot.. and it was only on one, so I don't think I just mis-saw something...

few visible scars