Imagine this scenario:
You’re walking through the park on your lunch break, looking for a place to eat your food.
In front of you sits a cute girl, alone, reading a book with glasses on.
Now you’ve observed she’s alone and reading a book, plus she’s wearing glasses.
It’s also during the day, in a park. So the situation is covered.
So you could mention something about her book, the fact she’s wearing glasses and she’s in a park alone reading.
How about something like this?
“Hey, sorry I don’t mean to be rude, but this is a pretty weird place to be reading 50 shades of grey don’t you think?”
“With glasses like those, you must be a Harry Potter superfan. Am I right?”
All you need to do is make sure you deliver those lines with absolute confidence, and they will work.