I don't have a single indirect opener that always works but here are some that work quite often.
I think an indirect opener is better even if it is obvious because it is just more polite.

With these they really won't know weather you are hitting on them:
- "Have I seen you somewhere before?". This is crucial to ask if you think they might go to your gym and are shy about seeing someone you approached at your gym.
- "Do you know where I can find a good coffee"? Then banter about coffee. This works better if you can say a specific coffee preference.
- "Are you about to go workout?" If they are in gym clothes
- "Do you know about anything fun happening in the city today?"
- "What does your shirt say?"
- "How long does this stop light usually take?" at the crosswalk
- "Is this line worth the wait?" In line.
- "Are you from around here?" If yes: "cool I live around here too". If no: "oh are you just visiting?"
- "what is in this building?"
- "What is this event?"
- "what are you going to take pictures of?" If they have a camera
- "Do you work at?" if they have company shirt. Also similar idea for college shirt.

These are just direct openers with the "you're cute" part cut out:
- "I was just on my way to work. Are you on your way to work too?" This can apply in pretty much any situation. Just swap out going to work with whatever you are currently doing.
- "I was just waiting for coffee and I saw you walk by. How's your day going?"
- "You just passed by me and if I didn't say something it would have been too late for me to talk to you". If you are walking opposite directions and she just passed by you, just "indirectly" do a double take, turn around, hustle to catch up to her, get in front of her, stop her and say this.