A few years back in the bike shop I was working in at the time, we got a recall notice regarding a specific model of tyre. Now, it was probably about 4 or 5 years ago, so before you start panicking, you probably don't have this problem now.
However, on arriving home from work today, I just noticed a thin, slightly uneven line running all the way around my rear tyre, a little off-centre. If I run my finger nail across it, I can just feel it. The line is a little darker than all the rest of the tyre surface. On checking the front tyre, I found exactly the same thing. Now, I would probably have dismissed it as nothing but for the memory it jogged of the aforementioned recall for a problem that started with just such an anomaly appearing. I think it was a Michelin tyre that the notice went out on. 70% sure anyway. I also think it was not PR2s, which is what I've got on there now. Again, maybe 70% sure. But what I do remember is that it pointed to a weakness or manufacturing fault in the tyre in question, maybe only certain production batches, again can't be sure of that, but it was of sufficient concern for the manufacturer to issue the recall notice.
Does anyone out there remember such an issue, did it affect you, did you receive a recall on your tyres for this reason? For now, I'm just going to keep a close eye on it, maybe it won't be anything to worry about.