I'm relatively new to trike riding, but here are my observations so far:
Recumbents are novelty out here in central Texas, and a motorists generally give me a very wide berth as they think that I take up more space than I really do. That's a good thing!
But, I suspect that motorists (as well as serious cyclists), see me and think that I'm somehow handicapped. Some motorists think that I shouldn't be on their road (go to YouTube and search for "Recumbent Has A Close Encounter With A Cement Truck" - I posted that yesterday.
Living in Sun City, I have to deal with more elderly motorists and golf cart drivers who leave their turn signals on, don't wait their turn at intersections, etc. and I get advice/grief from them who insist that I should have a flag on my trike. I do fly a flag, but only to appease my wife. My view is that if a motorist can't see me without a flag, they're not going to see me with one.
But then, I have to consider the possibility of being in an accident - not having a flag my be construed by investigating police as a contributing factor, especially if the motorist claims he/she didn't see me. So, there it is. But at least I can sport a little attitude - I live in Texas, but was born in Mexico, so I fly a Mexican flag! AARRIIBAAAA!!!!