I never applied for the express lane, so was dumbfounded as to why I was on the "nice" list, but walked through and enjoyed it.
Next flight, I had to go through the whole rigamarole. I told them last time I had qualified for the express lane, what had changed. Nobody could give me an answer other than to inform me that I was no longer on the list, for equally unknown reasons.
Other than being a little taller, having more hair and a slightly darker complexion, I am about as average looking as can be for a 60 year old guy.
You got "TSA Precheck" for that... service.
Two ways to get it - one, apply, pay money, lots of it (? $500 ballpark?) get investigated and fingerprinted.
The other way, it is random, available to all pax.
Either way, it is on your boarding pass when you have it - a paid-for persistent "privilege" or just a one-time random thing.