At my Japanese employer salary assignments are done by grade and there is essentially no deviation for individuals. The company does not have managers ask engineers whether they are getting paid enough, because engineers rush to say "I am thankful for the opportunity to work here and am glad to be paid the same as every other engineer in my grade." I have said it myself.

Then once a year when they recalculate grades, they tell the I-can't-believe-its-not-a-union "Do an anonymous survey and tell us what people actually think." They even follow the recommendations a portion of the time.

I love your stance on not doing anything formal. But if you took an anonymous survey of all the American engineers at my company, you'd probably hear "Do anonymous surveys or people will give you the answer they think you want to hear" from 100% of them. (Population size: 1)

Also, convenience samples have some well-known issues: if somebody was totally soured by their experience and cursed your name, would you still be talking to them on a regular basis? (My company has the same issue with its salary survey, incidentally: the people who are most dissatisfied with the amount of money offered no longer work here. Funny how that happens.)