According to https://history.stackexchange.com/questions/74386/what-is-the-origin-of-the-no-symbol https://history.stackexchange.com/questions/74386/what-is-th.

According to https://history.stackexchange.com/questions/74386/what-is-the-origin-of-the-no-symbol https://history.stackexchange.com/questions/74386/what-is-th... it was developed by a subcommittee of the convention, apparently from scratch (or at least, from signs that didn't have a slash).