The Witchers Hats are the cameo characters from Pajama Sam in "No Need To Hide When It's Dark Outside". They are cones that sit in front of the end of a railroad track.
The Witchers Hats appear only in the Secret Mines storyline. After Sam and Bert the Pencil complete the unfinished project in the mines, the construction crew arrive to blow a hole in the wall and make a way inside the abandoned part of the mines. Bert chooses to rejoin the crew and says goodbye to Sam.