I have an unknown brand two handle mixing valve in my shower. The handles do not have screws or allen screws to hold them on. There is a 3/8 inch slot in the handle perpendicular to the stem which looks like you can insert a screwdriver blade to release the handle but I'm not having any luck. I need to remove the handles to replace the washers and/or seats to stop it from leaking. Any thoughts on what brand it is or how to remove the handles?

It turns out this is an Eljer shower mix valve. The handles are released by inserting a screwdriver blade in the slot and that depresses a circlip inside. You PULL on the handle and it slides off, exposing an inner handle connected to the stem with a screw. Remove the screw and the inner handle comes off like most others. The seats require a special Eljer seat wrench and it will remove them easily by inserting it in the seats and turning counter clockwise.

It turns out this is an Eljer shower mix valve. The handles are released by inserting a screwdriver blade in the slot and that depresses a circlip inside. you PULL on the handle and it slides off, exposing an inner handle connected to the stem with a screw. remove the screw and the inner handle comes off like most others. The seats require a special Eljer seat wrench and it will remove them easily by inserting it in the seats and turning counter clockwise.
We thank kamerzel for the information. Tom