No, the warning sign certainly doesn't stop all from attempting the descent and climb back up. And you're correct the picture was taken part way down. I had to do this so one can see the bottom. If you stand at the top the drop is so steep you cannot see the bottom so if you want a picture of the shoreline you have go down part way.
There is another place in the UP that is very similar only not as high with similar warning signs.
I did attempt this a couple of summers ago. Like the sign says it only took about 30 seconds or less to get down. However, while my niece and nephew made it back to the top in about 15 minutes it took me all of 30 to make it back to the top.