These were made by Borland. Genuine examples exist for a few denoms in other colors. All the Borlands are notched. For more info see article (which needs updating - reminder to me!)
http://www.marlowcasinochips.com/links/davidspragg/borland/borlandhotstamp.htm

In any event, chips from this place are few and far between, genuine or otherwise. These are $30 each or $175 the set of 7 shipped. I only have two sets plus a few dupes. Ex Jerry Walls stock. I dont think there are any more around.