Kind of interested to know why a few yachts I've seen recently fly a numeral one code flag from the back stay.. ??
View attachment 196917
Excellent - that answers it... the boats in question were on YouTube channel 'Sam Sails' and he's in Heligoland at the momentDepends on where you're sailing.
In my experience it's mostly Dutch and German boats who fly pennant 1 to indicate they are singlehanded.