I just thought up another different possible way to cue the player into the difficulty of a fight: If the music is different for different difficulties of fights, so one theme for an easy battle, another theme for a normal battle, and a couple more music themes that tell you "uh-oh, this battle is going to be tough", although it'll probably take a couple beatings to learn the connection. Plus, it won't work with boss fights or other instances that use unique battle music.
Okay, maybe music on its own won't be a solve-all for knowing when to escape, but in some instances it could work as an instantly identifiable cue to run even without looking at the enemy stats.
Slightly related I wonder if the escape mechanic will be disabled for certain story fights that shouldn't be possible to escape from (or you can't run from), such as the final boss.
