There are no options.
So you have to manually click the lock at the top of the chat.
I have not found anyway to permanently accept fingerprints either, so you have to do that each time.
For security encrypted chats are not logged and if you put your iDevice to sleep the encrypted link is broken and buffer is destroyed so you will not be able to see that part of the previous conversation.
This is the first implementation of OTR and it's not perfect. I have faith that Shape will address some of the problems.
The one thing that you will find troublesome is that when you put your device to sleep it does not appear to notify the opposite end that the encryption has been disabled. This results in any messages they send being lost as you will not be able to decode them when you awaken the device. This makes sense from a security perspective but it would be nice if it had a way to alert the opposite end that encryption had been broken.
Sig? I dont need a sig, I need OTR