What's the opposite of the idiom 'red flag'?

A red flag often refers to a warning signal, usually used in medical diagnostics or for rating the creditworthiness of customers at a commercial bank. But what would be the (possibly idiomatic) opposite of it?

Let's say I want to explain that a cancer diagnosed person shows some symptoms during a therapy that may be seen as positive signals for the therapy leading to full healing.

The patient shows symptoms that are positive signals for full recovery.

Or I want to acknowledge a person's marital status, yearly income, employment period as positive signals that increase the probability of finally granting them a loan.

The customer's long-time employment is a positive signal for a high creditworthiness.

This is my first post on ELU. Please help me to make it better if I missed someting.

Solution 1:

You can use the phrase

"Green Flag"

Since the phrase Red Flag comes the railway semaphore signal meaning an immediate stop, it's opposite version there is the green flag.

While the term green flag is not included in any dictionary as of yet, it is commonly used.

You could say

His credit score was a green flag for the loan sanction.

Solution 2:

All-clear -- ODO

(noun) A signal that danger or difficulty is over.
"she was given the all-clear to travel home."
"The procedure was a success and Bob has now been given the all-clear."