Hey, That's it!!! Jacob Diehl
Vielen, Vielen danke. Udo!
I tried to figure out if any of these two surnames could match the letters by looking at the pictures, because the real size of this stamp is really really small. Suddenly I remembered I bought a big magnifier lens for precission work about a week ago. And now there's no doubt. I can see it clearly now with the lens. Jacob Diehl.
I'm quite happy today, I bought this guitar about a year ago thinking it was built around 1910 or 1920 and continously tried to find any hint about its origin... so it's from Germany... and built before 1875! What a nice surprise.
I'll be thankful for a lifetime, Udo. Big big thanks from Spain.
GruÃ.