I use a red Sharpie to write "Chase" and "Amex" on the fronts of both cards. I use the Chase for restaurants and the rare occasion when I have guests. I use the Amex for when using lounges by myself. Figure I'm less likely to be flagged as being abusive by either with that strategy.

I also have my own airport rituals (e.g. order togo lunch at Yankee Clipper (Chase), then get breakfast at the Centurion (Amex), pick up at YC, then head to the SFO UC closest to my gate (United) unless it is an evening flight and I have time then get free beer at the Giants Clubhouse (Chase) etc.)

Sometimes I wonder how granular the data looks: does Chase know that I went to two PP establishments on the same day at SFO, or that their customers used 2,000 visits in a month at SFO, and I used seven globally etc? Amex sure knows how many times I visit Centurion lounges, what class of air service, destination, airline and time. Wonder if someone who, say, spends $12k/year on their Plat, but has weekly UA J flights SFO-JFK is more likely to get a Centurion invite vs someone who spends $24k/year on their Plat, with weekly OAK-RNO laps on WN.