Odd symbols displayed when volume changed on Samsung KS800

Return the Sonos System for that? Anyway...

This advice was given on another thread

It is possible to use the Smart Remote with your Sonos system. From the Samsung TV select from Settings, 'Sources' then 'Connections' and 'OK'. Next select 'Universal Remote Set up' choosing Optical as the type and 'Sonos' as the brand. There should be a test, if prompted select Yes.

Now simply head back to the Sonos app, selecting 'Settings', 'Room Settings', 'PLAYBAR', 'Tv set up and control', 'Remote control setup'.

Please also be sure the Tv is running the latest firmware.

I expect that after following the above you can now control the PLAYBAR volume from the Samsung Smart Remote.

Note that the symbols being thrown up on your TV are from the TV itself, and have nothing to do with the Sonos. The optical connection between the two devices is a one way signal, from the TV to the Sonos, so there's not any way for Sonos to be sending anything back to your TV.

Not to mention the optical connection is audio only, it transmits no video at all.

I too have Samsung TVs. If the symbol you're talking about is a white circle with what looks to be two 3.5mm headphone jacks, that's the TV telling you that sound is being routed to an external device and therefore the TV will not display a volume level indicator as it has no way to know what the true level is. Once I used the procedure mentioned above to add the Sonos as a "Home Theater System" to the Universal Remote, the smart remote works just fine to control volume level and mute. I haven't figured out any way to make the TV not display the "external sound" indicator, but that's a Samsung issue and not something to blame Sonos for.