Please help identify this vintage (but non-Lego) brick! It's time to play the "what brick is this" game, and this time our contestant is definitely non-Lego, yet vintage.  This brick was in a small lot of early-60's Samsonite Lego bricks, and I am assuming it is nearly as old as those.  

It appears to be CA plastic, has studs (but they are taller than Lego studs), and a stylized "S" logo of some sort in the center of the surface of the brick.  Inside are slots and sidebars, rather than tubes.  Here are some photos to help.
That is a Kawada Dia Block made in Japan. Entex and Sears imported those into the US in the 70’s and 80’s and repackaged them under such brands as Loc Bloc and Brix Blox. The “S” is actually a K on top of a D, which is the emblem for the Japanese toy company Kawada. Dia Blocks are still made and available in Japan today.