Trial and error #2
I changed number 71721075 to Roman numbers:
VII I VII II I _ VII V
Then I changed it to Morse code:
-.. . -.. .. . _ -.. –
Dedicated to DT?
DT – Department Tarn – Albi – Museum Laperouse – miniature of Boussole.
This is just a wild guess. DT could mean anything. “Data Transmission” for example.