On the TF300T model, specifically Android version 4.0.3 (stock ROM), entry of text into signs causes the game to hang and then crash. This could possibly have to do with the way the OS handles keyboard input. When Minecraft is started again and the world is re-opened, a blank sign is in spot where I placed it before the crash. I have sent a bug report via Android 4.0's built-in bug-reporting system, but I thought I would mention it here as well.
UPDATE: I have upgraded the firmware to 4.1.1 (still ASUS stock ROM), and signs no longer cause the game to crash. From the comments, I have determined that this is an error specific to Android 4.0.3/.4's virtual keyboard. I was able to update and circumvent this bug, but others may not be so fortunate. Therefore, this issue should not be closed until the problem is fixed for Android 4.0, as I am sure that many devices have not been updated to Jelly Bean.