Visual indicator for Escape mode

“Escape” mode is where you press ESCAPE and then some key combinations to do things, e.g. pressing ESCAPE → G → J takes you to the Journal page for today.

This is a lovely feature, borrowed, I believe from Vim.

The problem is that sometimes I forget to press ESCAPE or haven’t pressed it strongly enough. I then type G → J, but end up accidentally writing on the page. This happens quite a lot. (NB other people seem to have similar issues with Vim: I keep forgetting which mode I'm in - Vi and Vim Stack Exchange)

To prevent this, it would be great to have a visual indicator, preferably brightly coloured, to show you are in ESCAPE mode, e.g. a small symbol which appears at the top of the screen. (NB I think that in Vim one is able to active to show the mode at the bottom of the screen)