Spoilers ahoy for Journey to the Center of the TARDIS …
When the Doctor's message gets burned into Clara's hand at the beginning, we also get a good look at the rings she's wearing.
In the middle there's the one she almost traded for a flying jet-ski rental in Rings of Akhaten, and two more.
In looking at these rings, the chain-link looking one is the same ring Oswin wore in Asylum of the Daleks.
The simple band appears to be the ring worn by Victorian Clara in The Snowmen.
What does it all mean? She's not only the same woman but these pieces of jewelry have gravitated to her throughout time? Victorian Clara only had one and future Oswin only had one, but contemporary Clara has three; is she key Clara?
What's the origin of the third ring, the one Clara's mother gave her? Is there still another Clara we have yet to meet?
In any case, it shouldn't take too long after the Crimson Horror begins before Clara once again learns she's one of several mysterious iterations of herself. As soon as Strax shows up he'll probably say, "Sir, isn't this the same boy you wanted to tend to with the memory worm?"