I think it's evident in the post. Don't ask the reason -- it's never a reason. It's always an instinct. But if asked to elaborate. Women's writing I tend to find a lot more "balanced" and articulate. Men, in the other hand, just tend to post their thoughts without proofreading it for the 50th time. Men also tend to have a more assertive tone with to-the-point and concise language.
I don't know really. Most of the time when I read a post, I tend to have an image of the person in my mind -- which means I automatically judge the person's gender. And whenever it has been possible to check it for real through their profile, most of the time my instincts were right.
Except ... the, well, to put it in modest language (😛), the ones who'd themselves not know what to call themselves, even though they try to portray a 'manly man' type personality. Anyway ...