I don't have a photo, but here is a YouTube video with one in use:
https://www.youtube.com/watch?v=Fl5Saf2iVQA
Look at about 3 minutes and 35 seconds into it (plus other places such as 7 minutes and 17 seconds).
I did a screen grab of that and attached it as well.
On The Mariner 19, if you have a reefing claw you can pull the boom outward from the mast and roll the sail around the boom to reef the sail.
The claw goes around the boom and allows the sail to be rolled up inside it to accomplish the reef.
I don't see it as anything you would use with Jiffy reefing as they are two entirely different approaches.
Charles