.38 S&W brass without headstamp markings were not intended for small arms use. They were mfg for some other military use like artillery or flare ignition or something similar. Quite a few years ago there was a bunch of this brass sold off via http://www.govliquidation.com/.
Not to say it isn't usable as .38 S&W cartridge brass... it is.
http://www.govliquidation.com/c/fire...-_-fired-brass