I haven't used an indicator (at least as you mean it) but my floating line has a red braided loop on the end. I've often used a long leader (usually straight 5 or 10 lb mono) where I fish a nymph or jig and watch the braided loop closely. I'll do short strips and let it sit for a minute. If I see it twitch, I set the hook and often have a b.g. This is especially true in the winter when the takes are much softer. So yes, in a way I've used an indicator.

TxEngr