At first glance, just a bunch of common brown Thomas pintypes. What makes these unusual is all have a marking consisting of a letter followed by three numbers on their crowns, as you can see in the photos on top. I have had these for a long time, and have never seen any others. Does anyone have any other examples, other U numbers or letter and number combinations? Left to right: U-463, U-170, U-628, U-296.