When applying for a Bank of Communications credit card, it shows that the signed card number already exists. This is caused by an application error. The application method is:

1. First, open Baidu and search for "Bank of Communications Credit Card".

2. Now we are at the Bank of Communications credit card application page, where there are many choices. Then select the type of card you need. Here we take the standard card as an example.

3. Fill in your basic information, including your name, ID number, etc. Then check "I have read" below, and then click Next.

4. Now enter your mobile phone number for verification. After verification is complete, click Next.

5. Then, complete the supporting cardholder’s detailed information.

6. Finally, check your information again. After verifying that it is correct, click Submit.