One of the scariest parts of identity theft is that it can happen for weeks, or even months, without you being aware of it.

According to Javelin Strategy & Research, 15.4 million U.S. consumers were victims of identity theft in 2016.

However, the sooner you are aware of the crime, the less damage the thief is likely to do to your credit. By being aware of the subtle signs of identity theft, you can immediately put a fraud alert on your account with each credit bureau to prevent the thief from opening more accounts in your name. While some signs of identity theft are relatively obvious, such as withdrawals from your checking account or charges you didn’t make on your credit card, others are more subtle.

Here are 5 signs to look out for:

1. You get a call from a collection agency about an account you didn’t open. It’s easy to simply assume that the creditor has the wrong number or made a paperwork mistake if you get a call about an unfamiliar credit card or loan. However, collection calls are actually a red flag that your identity has been stolen.

2. Your mailbox is empty. If you stop getting mail, you might shrug it off that the mailman delivered it to the wrong house, but if it continues for several days, you need to take action immediately. One identity theft tactic is to forward mail from the victim’s house to a location the thief has access to. This way, you do not see bills for the accounts they opened. Your first call should be to the post office, and then your creditors, says CreditCard.com.

3. A refund check arrives from the IRS, but you have not filed your taxes. It’s easy to simply be happy with the refund, but this likely means that a thief filed a return in your name. Another sign is getting a letter from the IRS that you filed two tax returns, when in reality you only filed one. You will need to file a Form 14039 Identity Theft Affidavit with the IRS to correct the issue, in addition to taking the standard steps to stopping identity theft from continuing.

4. You apply for credit and are denied. When someone takes out a credit card in your name, they are not paying the bill. This means your credit takes a hit for late payments, which can then result in credit and loan applications being rejected. If you know you have a good credit score and are turned down for a card, your next task is getting a credit report to find out if there are accounts you did not open.

5. Your child gets credit card offers in the mail. Child identity theft has been on the rise in recent years with approximately 1.3 million victims annually, 50 percent of which are under the age of six. If you find pre-approved card offers in your mailbox addressed to your child, your child’s identity may have been stolen. To find out if it was an error or identity theft, check to see if your child has a credit report. If there is a credit history on file, it is likely that your child has been a victim.

Time is of the essence when it comes to identity theft. By being aware of the signs and taking quick action, you may be able to reduce the impact of identity theft to your credit.