I look for other women on a team. If there aren't any women on the team, I would wonder why. Have other employees harassed former female team members until they quit? If there have never been any former female team members, that presents a problem, too. The men working there may not feel accustomed to and comfortable working with a female peer. Whether you're a "token" woman or you're hired on your own merit, sometimes male coworkers will view you as a token woman if you're the only one there. Look at all of the hostility from men on this post about the subject of trying to hire female workers. These are the type of men you could be working with when walking onto a job where there are no other women.
And besides that, it tends to be less unpleasant being the only woman on a team if there is more female influence there than just you. Men who view women as a threat are more likely to harass their female coworkers if there's just one than if there are several. Maybe they feel like getting rid of one woman is easier than getting rid of a bunch of them. Or maybe they just soften as they interact with women. Either way, depending on the culture, it can be difficult to be the sole female member of a team. Maybe there aren't any sexist men there, but being an outsider, you just don't know whether there are or aren't sexist men. Just because the people involved in hiring aren't sexist, it doesn't mean that team members aren't. And often times, the managers aren't aware of sexism on the team. It's not like they do psychological evaluations on their employees. And no one is going to raise their hand and say, "Yes, I feel threatened by working with women as equals and will harass them day in and day out just for the fun of it."
As an aside, a lot of companies think everyone wants to hang out after work and play Foosball and Xbox. I have a husband and other women might have things like children. It's a job, not everything there is to life.
Also, to the men here, proactively hiring minorities isn't illegal in the US. In fact it's encouraged. Ever heard of Affirmative Action? Where a segment of society has been discriminated against, you have to take proactive steps to change the discrimination, not just ignore it and hope it naturally disappears. Although women are technically the majority of the population (I've heard this argument before), in terms of power and social status, they're still minorities.