On the rare occasions when I catch up another cyclist, and he needs to pull out, then I too sit in super-primary, but call the word 'clear' to the other cyclist. Otherwise, he'll look round and see me, and think that I'm about to overtake - whereas I'm just holding on his wheel for a bit of a slipstream.
If it were me infront I wouldn't have a clue what you meant by "clear" and so I'd just ignore it. It's also doubtful I'd be able to hear you with headphones on. You could have said "Keep clear" or "It's not clear" and I could have misheard (even without headphones).
If you were following and I wanted to pull out I'd expect I'd throw a hand slightly out to indicate my intentions, look back to make sure you've seen it and you're not romping up the outside, and then go.
If you were following and were sitting further out in the road blocking my view behind I'd probably either push hearder to drop you, or ease off slightly in the hope you'd go past me. If you didn't then I'd put a sprint in. I prefer to see what is coming up behind me.
I'd have also hoped I'd seen you coming up behind me on the last few checks over my shoulder and I'd be able to have a guess at whether you were likely to overtake or just wanted to sit on my wheel.
I think it's a sign that the RHS bar end plug has fallen out and so I might have to replace it with a bar-end mirror (these are drop-handlebars).
