The following two pictures show a side-plate logo on a 1917 .38 M&P .
I find the size of this logo interesting. Notice that it is a little bit shy
of 0.500" wide. And notice that the 'Trade' and 'Mark' on the top and
bottom of the circle do not have a box around them.
From 1899 to 1910, and perhaps later, the side-to-side measurement
is at least 1/8" larger - at least. And the 'Trade' and 'Mark' are boxed
in. Thanks to DWFAN, here is a 1902 1st-change 32-20 :
At some point later, early 1920's, there appears to be a somewhat
smaller logo - as in this picture :
And then, several years later, we encounter very small logo's,
measuring about 5/16" side to side, and also with no boxing around
the 'Trade' and 'Mark' . This occurs in the early 1930's, but may be
earlier than that.
Finally, just to make things interesting, DWFAN has a post-WW2 pre-28 example:
Regards, Mike Priwer