I put a flag on it - I put a flag on it means you're saying it's yours and you're

I put a flag on it means you're saying it's yours and you're not letting anyone else have it

I put a flag on that last soda. You can't have it. I'm gonna drink it and you're gonna suffer.

She put a flag on my favorite chair. Now I have to sit on the floor.

I put a flag on that shirt. It's mine now. You can't wear it. I'm not letting you.