Nice sign and the way it's worded feels like it goes back even earlier. The electric light may well have been from lead-acid batteries, occasionally charged by a small generator, which was the state of the art for big houses for a while. Now come back around again with solar panels and power packs.
I was curious so did some searching and came across this:
https://stumbles.org.uk/Stumbles/index.html
The younger son Percy lived at Torcross where heowned and ran the Slapton Sands Hotel. He died about 1930
It would appear the Stumbles family were well-known in the Salcombe area, owning various small businesses, and that a Percy Stumbles is recorded there as running the hotel. I did some census searching but could find no references to Percy, but only 50% of the records have been transcribed on FreeCen for the 1891 (when he was either not born, or only very recently born) census, and very few records transcribed from the later censuses. It's unclear to me whether the Percy mentioned must have passed away for "Mrs A. P. Stumbles" (one presumes his wife) to be named as the proprietress, or whether that would have been the norm with the proprietor around (although I tend to think not).
Given the reference to the GWR motor-bus, which Wikipedia informs me ran from 1903 to 1933, and was introduced in the Kingsbridge region in 1904, I'd put the sign perhaps somewhere in the early 1930s, then. Interested to know anything else that might help narrow the dates, although I don't see any further useful clues in the sign itself.