Can I change from this:
low resolution language icon to this:
I do like the lock-screen version more.
Ask Different is a question and answer site for power users of Apple hardware and software. It only takes a minute to sign up.Sign up to join this community
If you just want to get rid of the flag, you can use the identical ABC input source instead.
If you make a copy of the US layout with Ukelele, you can add any icon you want. If you do not provide any icon, just the .keylayout file, then you should get exactly the "simpler icon" you show in your question (except the US will come after the icon).