What is wrong with genuine, non-materialistic appreciation? Why need to bring gifts to strangers prior to you knowing them?
And the ‘they know who I am’ argument.. Really? They do not know you as a person, they know you as a membership number.
I always find that genuine interest in people and a sincere thank you goes a lot further than anything else.
This week I found myself on a J flight to the Middle East where the passenger behind me was throwing a tantrum about something completely insignificant while still on the ground, and it was clear that he had a disrespect towards women. I asked the crew member who was being targeted to ask her supervisor to come talk to me at his convenience, because this was an absolutely unfair situation - I gave them both my contact details in case any complaint would be filed, and said I would like to present my perspective in such event, Not only were they extremely appreciative (supervisor took her side 100%) and she was close to tears of joy for me standing up for her.
To me, that is sincerity. Be kind, respectful and sincere (and not creepy) - that will help make the world a better place.