Stenciling says “6 & 7TH / PDE & 3RD” It’s the only pink tie on this track.
It’s marking the joint between two track segments. Look just above it. On both tracks there’s a series of bolts indicating that two track segments have been bolted together.
Not sure why the other joints aren’t marked.
if that was an insulated joint for track circuit separation there would be cables attached at each side and the two bolted plates would be aligned?
You can see 3-4 wires connected on either side of the plates.
I’m not sure if those particular plates are insulating connections though. Doesn’t really look like it, but I’m no expert on rail connections.