E70S-6 does not exist as for as I know. You may be refering to E70T-6 which is a flux cored arc welding electrode. The ER70S-6 is a solid electrode that could be used in gas metal arc welding (MIG) as wire or gas tungsten arc welding (TIG) as a rod. Hope this helps.
Actually the "E" stands for "electrode". There are two separate American Welding Society standards covering welding wire for flux cored arc welding and gas metal arc welding (MIG to alot of people). The "R" I have always associated with "Rod" in my mind. Welding wire that is made for MIG can be cut into straight rods for gas tungsten arc welding (TIG). The "S" indicates solid and "T" designates tubular such as used in flux cored arc welding. I do not know of any designation that has an "S" in it, without going with "ER". Therefore there is an ER70S-6 but I do not know of any E70S-6.