Hi Gunter,

you need to go under the "Construct" Menu to the "Curve" Icon and then select the "ISO" Icon with "V" settings only and select in the right view your object and move the yellow ISO curve until it matches (snaps) the position of your outer curve.

After that is done your create a small circle (as profile) for the "Sweep" Command were you use the ISO Curve as rail and then do a boolean subtract, to obtain the engraving.

Hope my explanation is clear enough.

Regards
Stefan