Cooter Brown might be on to something here.

Also, I dug into my Iver Johnson book I have and they had a few pictures of these pistols. I was mistaken in calling them the Special Agent model. The one I was thinking of is actually called the 'Secret Service Special'. I was going from memory and didn't look in my book. Sorry about that.

Here are some shots from the Iver Johnson book that might be helpful:

Barrel markings: Top of barrel has "38 Smith & Wesson Ctg"


Iver Johnson models of Secret Service Special


Meriden Firearms hammerless model:


Hopkins & Allen model:


All these models have the same markings on the barrel. They came in 32 S&W (6 shot) and, as seen from the photo, 38 S&W (5 shot). Barrel lengths seemed to be from 3" up to 6". The Howard Arms model I have seen had a 6" barrel and must have been made by Meriden Arms Co, as it had the same front sight as the hammerless one pictured here.

Sorry for the confusion and I hope this helps a bit more with your question. If it's from the 50s-60s, it's probably a cheap Spanish import. If it says 'Special Agent' on it, then it is certainly not the one I have been talking about.

I also don't think S&W made any top break models after about 1940.