Threema has a system where contacts are verified using a QR code scan: https://threema.ch/en/faq/levels_expl These three dots are shown throughout the UI, so with the identity of a contact you always see the trust level.

This is much easier to explain to a non-techie than comparing security numbers or hashes.

- Red = No trust

- Yellow = You trust that the server has verified the identity

- Green = You have verified the identity yourself

(Edit: Formatting)