Unusual S&G Dial Ring

There is an auction on eBay, item number 330666299255, for an S&G combination lock with an unusual dial ring. It looks like there is a tab at the top of the ring that can be pushed down into a (presumed) notch in the dial, to facilitate daylocking and/or discourage dial movement. I haven't seen this before from any manufacturer. Could somebody shed more light on the feature? Is there an S&G part number for this?

Thanks!

P.S. I could post the eBay image here, but I am not sure if that violates forum rules.

This is an image of the dial ring:
Attachment 5215

The lock is shown upside down. The tab should be at the bottom and would pull out for a padlock giving dual control. I remember when the those plastic head keys came out so it can't be too old. But I think the idea goes back further. Doug

The lock wasn't patented until 1979 but the dial would not necesarily be originally with the lock.