I think its a bit tacky alright! That or "bud" or I even heard a colleague trying to get the attention of a customer by going "yo yo"!!!!
Sir/Madam grand, its suitable, better then making some random gesture. If the person turns out to be chatty or particularly pleasant at every encounter then check his/her name on the manifest and remember it so you can refer to them by name. Always the most professional way if you ask me (obviously impossible to remember all customers names despite what my airline suggests! LOL)