Could the man third from right on the top row be your HBW?
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If you want to do some research, you can look up MWA, which is the acronym being spelled by the axes. A quick search pulls up lots of MWA acronyms.
Could it be the Mystery Writers of America? They don't look like authors.
Might they be the Missouri Whitewater Association? It didn't exist until 1970.
The Millennium Wrestling Association? Don't mess with an ax-wielding wrestler!
How about the Married Women's Association? I don't think so.
Are they the Michigan Wolfdog Association? Touring Forsyth?
The United States Department of Agriculture's Natural Resources Conservation Service -
http://www.mo.nrcs.usda.gov/partnerships/mwa.html - says the Missouri Watershed Association (MWA) is an organization that was formed as a Missouri Nonprofit Corporation to support watershed projects. Might this get you closer to an answer? I'm not sure of the history of this MWA, but their description sounds like it might apply:
The purpose of the Association is to promote all reasonable measures to conserve soil and water; to educate, encourage and carry out watershed protection programs for the prevention of floodwater and sediment damage; and to further the conservation, development of agricultural water management, irrigation and drainage.
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Of course, those guys might just be throwing everyone a big kiss:
mwa!