It very much depends on how you want to approach it.
You could come out and tell them straight out. Explain that it's part of your MH stuff, and that you're doing better than you have been, but that it's a part of you. You don't even have to come straight out and tell them, perhaps you could wear short sleeves when you see them at some point, and see if they react? It may be that they don't mention it, and that it doesn't phase them at all, or it may be that they ask without trying to be too rude. Remember, you don't have to tell them everything. You can tell them that it's to do with your mental health, but that you don't want to talk too much about it.
As for the people staring thing, I know what you mean, but I find that people don't actually stare as much as you think they would. Generally, people just notice, and then move on, especially when they are on holiday. At the end of the day, you're going to be abroad, and nobody there is going to know you, so what does it matter?
