[Milsurplus] 26003A Key - more

[Hubert Miller]

I thought i'd take a look for any maker name on the key. Somehow i overlooked the bottom of the key.
The text font on the bottom looks much later than i thought the key was. It looks 1940s and later. But 
there is no letter prefix, maker code, the C-- before the 26003A number. What i am not clear on still:

Do other 26003A keys not have the "DO NOT CLOSE..." text ?
Is this in fact, a signal lamp key ?
Is there a way to guess what decade this key was made?

-Hue Miller 
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