I'm sorry if I offended you or anyone else. Yes, I have bad days and last Friday was one of them. I should have just stayed off the internet. The button obviously exists, but I still have no idea what it does. I looked at all my sources and couldn't find the answer.
The button to re-set the safety clutch should be in the bed of the machine, as is the button to adjust stitch length. If you tip up your machine, the safety clutch is just under the button in the bed that is the furthest to the right. The safety clutch is mounted on the two connecting shafts just under the bed.
I just looked again, and your machine has adjustable needle feed to go along with the drop feed (the two feed systems working in conjunction with each other are called compound feed ) The only thing I can think of is that button is how you adjust the needle feed, but this is just a guess on my part. Why not send an e-mail to Singer along with the picture you posted? They will answer you eventually. Here is a link to contact Singer Industrial Products division: http://parts.singerco.com/html/contact.html