Sometimes when I walk in the city I try to make eye contact with women that walk in the opposite direction. I look in a neutral way without smiling.

Often it goes like this:
I am approaching a woman on the street as we walk towards each other. I look at her face in a neutral way without smiling. She does not look at me back, but she notices from the corner of her eyes that I am looking at her. And she starts smiling in a giggling shy way. Does this mean she likes you or does this mean nothing?

In other words: If a woman does not look at you, but she notices from the corner of her eye that you are looking at her, and she starts smiling in a shy way. Is that maybe a (small) indicator of interest (IOI)?

Edited: I made this post more specific.

What do you guys think of this?

Yes that is an indicator of interest.

Unless she specificly tells you 'go away' or just walks away without doing anything, it's a ioi

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To game at your best you have to be willing to do your worst.

Yes. She knows that you're checking her out, and the outcome is a positive one.