To answer the question - if it is not normally visible - there will not be a problem. If it is cultural it 'shouldn't' be a problem - if it is there are ways to deal with that. Have seen plenty of pilots with them, most wear long sleeved shirts, etc.
On a side note, who gives a **** if you have one or not. It is purely a personal choice - sure its associated with some sort of stigma, but as someone else mentioned, so is smoking, alcoholism, not to mention those guys flying around who have trouble sleeping in their own hotel room on EVERY layover and are addicted to any female (and in some cases male or both) that is not their wife at home.
Working as cabin crew, i'd say almost half would have one somewhere, but you'll rarely see it at work - they can get in trouble if you can.
I have one, got it on Venice Beach at the age of 18 (paid in Aussie $ as it was all I had at the time), never planned to get it. It's a set of wings I drew on the back of a History exam in grade 9 (for what its worth, I failed the exam and the moron teaching the class said I would never amount to anything), and I had kept it in my wallet ever since. It means something special to me, I don't regret it for a second - its a great reminder when things get tough.