Depression Era Rubber Stamps

I do love stamps, although this is a recent love.  I used to think that the stamp aisle at the craft store was only meant for scrapbookers, of which I am not.  Then, after a curious day at the store I became the new owner of several rubber stamps, including an alphabet set.  I was hooked.  I like to make my own greeting cards from vintage postcards and stamps work well for this purpose. 

I'm finding that I enjoy old stamps best, and I've picked up a few at estate sales, and antique stores.  So you can imagine my surprise when I came across this box of stamps at an antique store a couple of weekends ago.  The entire set of letters, numbers and symbols are accounted for.  The only thing missing is the ink bottle and pad. 

I brought them home and tried researching their history.   Why would anyone need stamps this size?  The big red box is not marked anywhere nor are the stamps themselves.  All I could find out is that they most likely date back to the depression era based on other examples I saw.  They were used in schoolhouses and general stores to make signs.  Two companies, Superior Type Company and Stamperkraft, manufcatured these types of stamps in the US and may have made mine.   Everything is done on a computer these days.  It didn't even cross my mind these would have been used for signage.  

I am happy to add them to my collection but I'd still like to know more information.