While I don't know the occasion for which these rounds were made, they were made a long time ago for the Railway Express Agency, a shipping company in the United States that, as I recall, took over Adams Express. The Railway Express Agency eventually changed its name to just its initials, I believe, "REA" and dealt primarily with shipments going by rail and by air. My mother worked in the Air Express offices of REA for years, in San Francisco, California.
I have four variations of this dummy. I have the headstamp you show with both chromed bullet (I believe they used .45 auto bullets in the making of these) and GM bullet. I have another with the chromed bullet, but the headstamp adds an exclamation point (!) after both the "REA" and the "AWAAAY" so it reads "HI-YO REA!AWAAAY!" Then, I have an all plastic version with the headstamp style without the exclamation points, and with raised letters (Probably made off of a mold of one of the original metal cartridges). Of course, the wording on the headstamp is a take-off on the words of a Western mythical character, The Lone Ranger, as he "rode off into the sunset" - "Hi-yo Silver, awaaay!"
If anyone knows what these commemorated (I am inclined to think some promotion for a new shipping program, rather than a milestone in the Company's history, but I could be wrong), please let us know. I have a sentimental attachment, since my mother worked for 40 years for that company. I seem to recall that I found my first one among my mother's stuff when she passed away in the early 1960s, but that could be wrong. Time plays tricks with the mind, especially since I am now older than she lived to be,