I can see how places like Wetherspoons, Nandos, MacDonalds, Burger King, and other big chains could comply with this. The sort of place where things come out of the freezer, into the fryer, and are counted onto the plate in standard portions.
But most places aren’t like that.
Small family run cafes, independent pub kitchens and the nicer restaurants would be unable to comply (not all scones come off a production line, and good restaurants change their menus daily or weekly to suit the seasonal veg supply, and two chefs can make the same sauce or home made ice cream very differently.
No, I won’t be signing.
The hospitality industry has enough to cope with at the moment, this would IMO be an extra unnecessary burden.
Although I do admit that where places include the carb content (Costas and Wetherspoons’ carbs are both online) I am curious enough to read the info, often with a horrified fascination (Costas!!!) but my goal is to choose foods with as close to zero carbs as possible, and I can do that by simply picking meat, fish, eggs, green stuff and herb teas.