I'm doing this in the community where I live and I have discovered that it is super effective. I send an email to each company explaining a security problem with their site (currently focusing on simple lack of HTTPS for form data, and not mentioning the public disclosure because I want to see who fixes things because they care vs. those just avoiding negative publicity) and if they haven't resolved it or replied within a week, I list them publicly on
https://www.insecure.org.je.
The site isn't winning me any design awards and needs expanding of the advice articles, but dozens of local companies are immediately spurred to action when they appear in the "Sites requiring extra caution" section. Thousands of local users have directly benefited by the added security, even though they are completely unaware of why it was upgraded.
The reaction from some business has been very predictable, with a mix of hostility, threats, confusion, outright lies, but enough respond politely and want to fix things, and I go out of my way to help those who want to learn.
Source is public and if you want to try this locally, I highly recommend it: https://gitlab.com/tombrossman/insecure.org.je