How to Identify an Atheist

Remove your preconceptions.  Atheists don't worship the devil (they probably don't believe in devils any more than they believe in gods!), they aren't axe murderers and they generally don't want to get in the way of your religious practices. With that said, atheists can be very spiritual people, seeking answers to the same Great Questions that theists do. The main difference is that they lack belief in the existence of gods.

• Atheism includes both people that aren't convinced that gods exist and people who claim that gods don't exist.
• Some atheists are religious. Buddhism is an example of an atheist religion. Many people practice religion without believing in deities.

Understand why you want to know if someone is an atheist. You will have much better luck getting atheists to "come out" to you by showing that you're interested in a different worldview from yours. If you show that you're trying to gain converts, well, you'll have worse luck.

Understand that they are most easily identified by what they don't do.  Some don't attend worship services (although some still do for the "community" aspect of it, most don't). They might not celebrate purely religious holidays like Easter, but they might for traditions' sake or they might celebrate the time of year and a public holiday.  When someone is hurting, they might say, "You're in my thoughts," as opposed to "You're in my prayers."  In general, their behavior shows a marked absence of belief in a deity.

Ask some questions about their life in general for "clues", if appropriate. If you are often in social situations where small-talk goes on, you can ask subtle, inoffensive questions that might reveal that someone has a religion, or that they don't. For instance, you could ask, "What are your plans for the weekend?" If they say they are going to church on Sunday, it's very unlikely they are an atheist! You still shouldn't assume though. Around religious times of the year, such as Diwali or Christmas asking about plans for the holidays could reveal beliefs. You can try to find out if someone is not an atheist by getting a group conversation going about where people were christened or baptized and lead it on to what they'd want to do for their children. You can ask about people's spouses if you think it's appropriate. Lots of people are happy to describe their wedding day, theoretically, the happiest day of their life, those that got married in a religious service, and still have that faith, are likely to be identified as not atheist during a conversation like this.

Understand that they tend to be skeptics in other areas of life.  It's likely that they take few things on blind faith, but you might meet the rare atheist who believes in everything but a god.  On the other hand, they are also comfortable with what they don't know.  With no way of knowing whether there is an afterlife, for example, they won't fill that void with something such as a deity.