Rust coloured spots on 4 year old

[Countrybumpkin19]

Just noticed these spots on my 4 year daughter's ankle. They are orange/rust coloured and almost look like tobacco stains. Any idea what they could be?

Ink of some Kind
Or henna?

She's been wearing socks and shoes all day, so hasn't come into contact with anything.

I had a weird yellow patch on my bum recently, eventually realised I’d sat on a yellow felt tip. Was there any colour on her socks?

We get marks like that on our clothes/feet from certain parts of our very crap back lawn.

Should have mentioned they don't scrub off!