Hello and thanks for reading my post,
those are stamps from guitar manufacturer, in cavities of pickups.
In order to track Maya Musical Instrument CO and Chushin gakki
history and guitar models I need to know what these kanji mean.
Both red and black one. If I "translated" it correctly part of it says "Yamada",
which is probably surname of guitar inspector.
Any help is precious to me.
Thank you.