Some years ago Nunatsiavummiut started making a writing distinction between their single and double (or long) ng. Even though all fluent speakers made the distinction in speaking, no one had been making it in writing. Nunvummiut and Nunavimmiut make the distinction as follows.
single: ng double: nng
The school board in Nunatsiavut started using:
single: ng double: underlined ng
Lately there have been some publications in Nunatsiavut that used:
single: ng double: ngng
I personally don’t care whether it is the underlined ng or the ngng that is used to represent the double version. The most important thing is that it be marked. People can use nng, underlined ng, or ngng. Not marking it does cause a problem though. Learners will not speak properly.
I do note that I can’t figure out how to make an underlined ng on this blog – yet.