In Orienteering, control (checkpoint) markers tell you that you have found the checkpoint shown on the map. They also may include some mechanism to record that you visited that checkpoint. Here are some options for control markers:
Control flag with manual punch - punch your answer card in the correct box. These can be purchased for around $10 each at an orienteering supply store.
Stickers - bring an answer card with you and place the sticker in the correct box
Streamers labeled with a code - bring a pencil and answer card with you to write down the code. We use regular flagging tape and sometimes clothespins.
Electronic timing - carry a timing card with you and tap an electronic box at each checkpoint.
Materials & tools
1 inch internal diameter PVC pipe (big enough that the punch stores inside the pipe)
4 inch wide stripped reflective tape that I got off the web somewhere, maybe Tape Jungle
Length of nylon cord for hanging.
punch
PVC pipe cutter
Assembly
Wrap the tape around the pipe before cutting
Cut pipe to 7" lengths using a PVC pipe cutter
Drill holes for the cord.