It just means the key is an ADK, and designated as such.
If you have some keys that are not showing the red circle with the cross, you can always reach out and we can do a health check to see if everything looks good.
In my testing, I usually only see the red circle icon, so tough to say for sure what is going on with your lcients.
If you have clients and are checking in, and show the ADK, then you're probably good, but reach out to Symantec Encryption Support if you're wanting to do a deep dive to make sure everything is good.