Hi
As advised in your related thread, a good quality screen protector may be effective in obscuring or reducing the visibility of the existing mark on your Apple Watch, as well as in providing some measure of protection against future damage.
Note that some users have reported experiencing issues with touchscreen responsiveness when using a case or screen protector under the latest versions of watchOS.
If in doubt regarding compatibility (Zagg, for example, does not list protectors specifically for Series 3 models), then I suggest checking the manufacturer and also buying from a reputable source (such as direct from the manufacturer), who may offer a refund if their product does not work as intended (check before buying).
You may wish to consider, for example: