I often Wear a polo shirt at the non formal events at my sailing club. They normally have a 3 inch circle logo on the left upper chest saying something like "Three Rivers Race 2002", or "Yeoman and Kinsman Nationals 2016" The club is something of a heat trap as it faces south, fully formal dress in the summer can be quite hot.
I must admit I prefer a polo Shirt with collar, not a T shirt without, to me a T shirt is still underwear...