I made a note of the manner servant's hands are placed on the back of the chair in the painting in The Road to Württemberg.
Friedrich Ludwig, Crown Prince of Württemberg and his wife Henriette Marie of Brandenburg-Schwedt
This is how the hand on the back of the chair looks when enlarged. Is is rather fuzzy and doesn't have the expected contrast. I may have to do some work on that.
Below is how it looks like when re-oriented. What does it resemble?
No brownie points for this one. They are the antlers on the Württemberg coat of arms. The enlarged images are rather fuzzy so I have displayed the original size copy although it is much smaller. Perhaps it will good enough on a mobile phone.
What of this one in Meet a real live "Black" German Duchess of the 21st Century?
Is there some connection between the way the servant's hands are placed on the chair and the Mecklenburg crests? The tilt of his head brings to mind one of the bulls, although it is in the opposite direction.
David Matthieu was a student of Antoine Pesne (painter of this one). It stands to reason they will show some similarity.
It's a pity about the quality of these photos. There would be a lot more to see if they were bigger and sharper.