Polishing mixed metals vintage cuff

I recently acquired a ‘vintage’ sterling silver cuff with a strip of
14k gold as a gift for my sister. It is in need of a good polishing,
and I thought I would tumble it (since I don’t have a proper
polishing setup of my own). This brought up some questions.

The cuff is marked:

Sterling Silver
14kt Signet

Can I be positive that the gold strip in the piece isn’t a plating
that might be harmed by tumble polishing? What does “Signet” mean in
this instance?

Images of this piece can be seen here:

Thanks for any insight or caution.