ACR's (FE) is an abbreviation for ALUMINUM COPPER RADIATOR with iron or steel on them. Only a small amount of iron or steel is allowed to be on these radiators to be purchased in this fashion. They do bring a bit less $$$ than completely clean ACR's but it can save you a lot of work. If you lack the proper tools to clean this type radiator sometimes this is the way to go.
Note : If you bring these radiators in with the furnace or air conditioner still attached, if the recycling center accepts them at all that way you will typically receive scrap iron price for the unit. If the air conditioner or condenser unit still has the sealed unit (Compressor) and still has Freon in it you will typically be turned down for even selling it for scrap iron. Almost ALL Recycling centers wont accept any type refrigeration type stuff that has the sealed unit (Compressor) still attached or has Freon in it still. Always make sure these units are removed before delivery or Contact your Recycling Center to get more information. A lot of towns and county's have annual collection events for this type stuff but typically have a charge to you for accepting the refrigeration units that still contain Freon.