I was recently on an airplane reading Why I Am Not a Christian and Other Essays on Religion, by Bertrand Russell. I was concerned about how other passengers might feel if they saw me reading a book with such a title. So I tried to make sure no one could see exactly what I was reading. Is there a single word or short phrase that describes my hiding something out of concern for offending others? I haven't been able to come up with a word or short phrase that really works.
careful not to cause embarrassment or attract too much attention, especially by keeping something secret:
The family made discreet enquiries about his background.
They are very good assistants, very discreet - they wouldn't go talking to the press.
I like discretion (which is perfectly accurate), but given your location where sensitivities can run higher than most I'd offer
I would suggest a phrase solicitous discretion
solicitous: characterized by or showing interest or concern:
she was always solicitous about the welfare of her students
a solicitous inquiry
discretion: the quality of behaving or speaking in such a way as to avoid causing offense or revealing private information:
she knew she could rely on his discretion
Oxford Dictionaries Online
You may have just been self-conscious then.
self-conscious adjective nervous or uncomfortable because you are worried about what people think about you or your actions:
He looked uncomfortable, like a self-conscious adolescent.
I always feel a bit self-conscious in a hat.
Stop staring - you make me self-conscious.
You were cautious not to set of peoples sensibilities. One might even say you put on the kid-gloves to handle the situation with potential hostilities in a confined space. You were doing this out of prudence. It was a tactful move on your part.
cautious ADJECTIVE 1 (Of a person) careful to avoid potential problems or dangers:
kid gloves, phrase: handle (or treat) someone/thing with kid gloves: Deal with someone or something very carefully or tactfully
prudence NOUN [MASS NOUN] The quality of being prudent; cautiousness
tactful ADJECTIVE Having or showing skill and sensitivity in dealing with others or with difficult issues
Perhaps, the individual wanted to simply read her book and avoid confrontation with individuals who may feel passionately about the topic of Christianity and want to engage in conversations about the topic.
The word to use would be "Private".