I got a pin from AOPA for 30 years of membership which I paid for, so? They mailed it to me with a letter signed by Phil Boyer (no doubt not his real signature).
When ever I have to fly domestic I fly CO. I get good treatment, nice service, etc. Even if I pay more for the ticket, and I often do, I don't care. I like CO, and always pay a compliment to whatever crew is standing there when I leave the aircraft.
Now, does 20 years of paid service require some recognition? Not really, especially these days, BUT, if you are going to give recognition, do it right. Something worth doing is worth doing well. But, what exactly is the right way?
If I were the CEO of CO (CAL if you prefer) I'd take some time each month, maybe a few hours, and just sit there and personally sign a bunch of letters for those who have achieved a significant employment milestone with the company. 10 years, 25 years, 30 years, whatever. It does not have to be on the exact day, just during the same month. Yeah, my hand might be sore afterwards, but...
Then, perhaps, I'd have that letter along with the pin mailed to the residence of the employee. Yes, that would cost some money, but might be better than the alternative mentioned above.
Of course, as CEO, if I did that, I am quite certain there would be someone to complain that it wasn't "personal" enough.
Perhaps best not to do anything at all.