I have read somewhere in this forum that up to 2500C the version is stamped on the main plate, for version D is not.
Up to 2500C, the serial is stamped on the base of the balance cock (just above the "SWISS TWENTY-SEVEN" text, as in the following borrowed picture:
View attachment 1280043
On the 2500D it is stamped on the balance cock arm, like yours.
Also read that serails 8525xxxx and up are likely to be 2500D.
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