Hi ladyfaith24,
I found this font "Taranto" designed by Chris Corrado and published by Antitype. (2020)
Only S & D are modified.
Taranto was inspired by the typeface Domino by J. C. & M. Demarchi (published by Mecanorma in 1973).

Hi vknuever,
Indeed, I agree with you that it's an alphanumeric code, which should give a location in Belgium 🇧🇪, for example.
Do you have the GCXXXXX codes?
I'd like to have information on the geocache's description and the "hider," who could perhaps give us the alphabet used or made by him, or the year it was created.

Hi oddeyecircle,
Try this font "Gretel Crisp" created by Sylvia Janssen and Daniel Janssen (c) FOUNTAIN

Hi oddeyecircle,
Try this font "Gretel Strong" created by Sylvia Janssen and Daniel Janssen (c) FOUNTAIN

Hi oddeyecircle,
Try this font "Curly Qs" created by Natalie M.

My pleasure
Ang kasiyahan ko

Hi Dohoonie,
Try this font "Pink Chicken" designed by Scratch Design Studio.

Hi Dorian Grafika,
Try this font "Collegiate FLF" designed by Cassady & Greene.

Have you posted the entire mystery to be solved?
Is the image complete?
it's really interesting ...

The word "Kastelen" comes from Dutch and simply means: 🏰 "castles"
- ✳️ Linguistic details:
"Kasteel" = castle (singular)
"Kastelen" = castles (plural)

So "Kastelencode" is a portmanteau (or pun) that literally means:
🔐 "castle code" (or "code in castles")

Hi vknuever,

in another style, you also have this dingbat font "Black Castle" designed by Masyafi Studio.

Hi vknuever,

I know it's not exactly like your drawing, but You can try this one "Fontazia Chateaux 1&2".
This Font Family was designed by Denise Koehler and published by Deniart Systems.

Out of curiosity, where did you find these drawings? Perhaps they were your own creation...

Hi Electramagick,
Try this font "Portobesto Caps" designed by Katsia Jazwinska.

If we could go back in time we would see that it did indeed exist.
(http://web.archive.org/web/20200415191354/https://creativemarket.com/Jazwinska/1064613-Portobesto-Brush-Script-Trio)

Hi iSteph,
Try this font "TAN-Pearl" designed by TanType Co.

HI Bloxy,
Try this font "Xenosphere" created by Darrell Flood (Hawtpixel).

You're welcome

Hi leon bhowmik,
Try this font "Agabil" designed by Vunira.

Hi octania,
Tris this font "Selima" designed by Jroh Creative.

Hi octania,
Tris this font "Nightmare Street" designed by Christopher King and published by Wing's Art Studio.

Hola colegas,
Try this font "Typo Slab Inline" designed by Studio Typo.

Hi Luna Taisho,
Try this font "Cool Vibes" designed by KA Designs.