Thanks for the replies!
I'm not too sure whether it was attached to a metal or wooden pole as I just saw the sign itself and didn't think of the question at the time. The back of the marbles have worn away white paint on them, so I think you would be correct to assume that they would 'glare' at them as light refracted off of them as the driver went by. Scary, but no doubt convincing
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He's manager of a road maintenance company, so I'm assuming while cleaning around in storage he found it. The company is located in North Dakota, though I won't exclude the possibility of it originating in another state. Another thing I’d like to mention is that it could possibly be from the early 60’s as well, though it’s 100% steel so it probably wouldn’t be any later than that.
I didn't see any fine print anywhere on the sign, but I'm sure it could have been made by a citizen group, like you said. I'm not sure where they would find a machine to make the beveled lettering though.
I have found nothing having to do with the sign anywhere so far from my searches on the web as well. :unsure:
That's about all I can think of to explain it. Thanks for your help so far!