My first academic job, in 1974, was at the University of Illinois, where professors were state employees whose names and salaries appeared (with some delay) in the state budget. So, if you wanted to, you could go to the library (those were pre-internet days), check out the state budget, and study the salaries of all your colleagues.
As a result, at least among the young assistant professors, salaries were discussed freely. We would each get annual letters telling us how much we were appreciated, and then telling us about our salary for the next year, and we all treated those numbers as public information, knowing that they would indeed be public in a few months for anyone curious enough to look. That had some effect on salary policy: e.g. anomalies between new hires and previous hires had to be noted and explained (there was high inflation in those days, and the state budget often lagged behind the rate of increase in the new Ph.D. market, for example).
I subsequently moved to private universities (Pitt, then Harvard, and now Stanford), where salaries were not public and salary discussions were more guarded, and among closer circles of friends.
More generally, salary has long seemed to be one of the things that Americans are reluctant to talk about freely. But that may be partly generational, according to this recent WSJ story:
Workers Share Their Salary Secrets: Office Taboo Fades as Younger Staffers Openly Compare Pay; Wanting to Know 'Have I Settled?'
"Comparing salaries among colleagues has long been a taboo of workplace chatter, but that is changing as Millennials—individuals born in the 1980s and 1990s—join the labor force. Accustomed to documenting their lives in real time on social-media forums like Facebook and Twitter, they are bringing their embrace of self-disclosure into the office with them. And they're using this information to negotiate raises at their current employer or higher salaries when moving to a new job.
"Not surprisingly, many firms want to keep salary information private. They hope to retain the upper hand on salary negotiation and hope to keep flawed or even discriminatory compensation systems under wraps.
"But for workers, information is power, and young people recognize this. "People are much more willing to talk about pay than they were even 10 years ago," says Kevin Hallock, director of the Institute for Compensation Studies at Cornell University and author of the 2012 book "Pay: Why People Earn What They Earn and What You Can Do Now to Make More."
...
"Companies may not like transparency, but they cannot outright bar rank-and-file employees from disclosing their pay internally or externally, under the federal National Labor Relations Act, says Fort Lauderdale employment lawyer Charles Caulkins of law firm Fisher & Phillips. That means that an employee handbook or social-media policy barring workers from disclosing their pay is generally a violation, he says. (The rules are different for managers and supervisors, who can legally be prevented from disclosing pay.)"
...
"Lucy Bayly, 43, a copywriter for an advertising agency in Oneonta, N.Y.,
compares discussions about income with conversations about sex: "You're dying to know, but it's too rude to ask."
Such conversations run the risk of inspiring a corrosive kind of jealousy, she says. "You think you're satisfied and then all of a sudden, you find out someone is paid a little more, and it ruins your day because you start wondering, 'Have I settled?' "