Here's how I found out that a place I worked had ridiculous gender based salary guidelines. A man who graduated from the same school I did, a year after I did, with the same degree (snarkily I add that I had higher grades and more experience), who took the job I had held the year before as I moved into a different position, who was having his first year in the workforce, who had the same responsibilities that I had, was making significantly more than I. I was shocked! I was barely making enough to pay my rent and had taken a second job to pay for clothes and groceries and he was making almost 50% more in his first year than I was in my second. He was also shocked.
I asked a few other people in the organization if my experience mirrored their own (maybe the admin didn't like me or thought I wasn't doing a good job although my assessments wer top notch). It turned out that men were making significantly more than women across the board in this job regardless of years on the job, educational level, or competancy.
Several women with more time on the job than I brought this situation up with the admin and were told that those men had families to support. However, some of the men were single and several of the women were widows raising families.
At a staff meeting, the women were lectured that they were hired for their wages and the wages of others were not their concern. My concern was that their salary policy was not made known to us so that we could know what we were getting into.
What I had gotten myself into turned out to be a whole other can of worms. But that is how I found out that I was valued less because I was a woman.