No Apostrophe in Farmers Market?

“Here’s an even trickier one: farmers market. The market is used by the farmers, populated by the farmers, but generally not owned by the farmers. So it seems reasonable to conclude that you don’t use an apostrophe because the word farmers is there to identify the type of market. It’s an adjective.

I should note that there are credible people who firmly believe an apostrophe is required on farmers market, writers strike and similar phrases. It’s a contentious topic, and you may have to defend your choice to someone no matter which choice you make.”

http://grammar.quickanddirtytips.com/grammar-apostrophes.aspx