At least in the U.S., pink paint on the ground or features, pink flagging, or pink pin flags are mostly used by surveyors. Pink is used for its high visibility to mark the ground and it’s likely this paint isn’t meant to last long.This could be marking project limits of a railway survey, upcoming maintenance, or a construction project. There could be other ties painted, but I wouldn’t be surprised if they were miles away. It could be an indication of nearby ground control. Does “6 & 7th / PDE & 3rd” have any meaning locally? Could PDE be a street name abbreviation, considering that the other parts sound like street names? Railways are long and if it’s a limit of one project or the dividing line between two projects, some of those streets might be far away.