I use Ctrl-@, also known as Ctrl-Space or the null character. For another screen session that I run within a terminal in my main session (don't ask), I use Ctr

I use Ctrl-@, also known as Ctrl-Space or the null character. For another screen session that I run within a terminal in my main session (don't ask), I use Ctrl-]. (There's at least one keyboard/terminal setup that doesn't let me type the null character. When I use that, I temporarily change the escape character.)