Saw these in the Sparks yard and would like more detail on what they are exactly. The red "flag" I think identifies the track/train is not to be used, the yellow paint marks with the track centered tube I am guessing identifies the last spot a car can be placed allowing clearance with with adjacent track near the switch. Thanks in advance for your replies....
I'm thinking that the red flag is a stop point that must not be passed. You're right that the yellow marks a fouling point.
Sometimes fouling points like Hardcoaler said and sometimes they mark a stopping point for any number of reasons like a crew change spot, or servicing spot.