You walk into a coffee shop planning to be a total hermit behind your book while you enjoy a beverage. You see a blind friend hanging out with someone else. In such circumstances with a sighted person, you would probably make eye contact, smile and move on. However, that’s not possible in this situation. What do you do?
I can tell you what to NOT do under any circumstances. Say nothing at the time and then later tell the blind person you saw them. It’s creepy. And somehow demeaning. Oh, yeah, and it seemingly feels worse when you are female.
The better move is this: Walk past the table – not over, but past – and say, “Hey, it’s <name>. I’m just passing through.” Done. The reason, by the way, for the “walking past” part is that it provides the element of casual eye contact as opposed to a desire to engage in extensive social interaction.
People seem hesitant to offer a verbal greeting for fear that they will get sucked into a conversation. While that risk does exist along with the possibility of awkwardness, those should not be obstacles to doing the right thing. By approach, you can minimize the risk.
And, did I mention, it is otherwise creepy and somehow demeaning?