Marked Horn scales?

[Magpie]

Doing my first "frame off" restoration. Been working on the blade a while, and just got around to the scales. Using the old scale on the one side, and had to recreate the backside. Normally, I would not even bother mentioning this, but while polishing up the old scale I noticed something odd. pressed into the horn on the inside where it could not be seen are letters. I believe it says Sid these are not scratched in, but actually IN the horn. Anybody ever see this inside scales before?
And this IS my first time making horn scales, so feel free to offer up opinions.
What I learned with this task is, take off your shirt and sweater BEFORE you remove your respirator! Now I want to learn about Sid!