I got this interesting pair of messages from Schwab recently - not sure if any other companies do this

On login:

Schwab Watch out for scams. DON'T share this security code with anyone, EVEN IF THEY CLAIM to be from Schwab. Your code for online login is XXXXXX

And then on a later phone call with an agent:

Schwab: XXXXXX is your Schwab security code to confirm your identity with the agent.

This is a nice touch, though I'm not sure how much it would help in a real scam situation for say, my grandma.