签名证书：由权威颁发机构颁发给服务器或者个人用于证明自己身份的东西，默认客户端都是信任的。主要目的是用来加密和保证数据的完整性和不可抵赖性
自签名证书：由服务器自己颁发给自己，用于证明自己身份的东西，非权威颁发机构发布，默认客户端都是不信任的，主要目的是用来加密和保证数据的完整性和不可抵赖性,与签名证书相同.
详细具体解释见下面英文。
When you're building an ecommerce site one of the first things you'll need to set up is a security certificate so that your server data will be secure. When you set this up, you have the option of creating a self-signed cerficate or creating a certificate approved by a certificate authority.
Similarities Between Signed and Self-Signed Certificates
Whether you get your certificate signed by a certificate authority or sign it yourself, there is one thing that is exactly the same on both:
Both certificates will generate a site that cannot be read by third-parties. The data sent over an https connection or SSL, will be encrypted regardless of whether the certificate is signed or self-signed.
In other words, both types of certificates will encrypt the data to create a secure website.
Then Why Pay a Certificate Authority?
A certificate authority tells your customers that this server information has been verified by a trusted source. The most commonly used Certificate Authority is Verisign. Depending upon which CA is used, the domain is verified and a certificate is issued. Verisign and other more trusted CAs will verify the existence of the business in question and the ownership of the domain to provide a bit more security that the site in question is legitimate.
The problem with using a self-signed certificate is that nearly every Web browser checks that an https connection is signed by a recognized CA. If the connection is self-signed, this will be flagged as potentially risky and error messages will pop up encouraging your customers to not trust the site.
When Can You Use a Self-Signed Certificate?
Since they provide the same protection, you can use a self-signed cerificate anywhere you would use a signed certificate. But some places work better than others.
Self-signed certificates are great for testing servers. If you're creating a website that you need to test over an https connection, you don't have to pay for a signed certificate for that testing site. You just need to tell your testers that their browser may pop warning messages.
You can also use self-signed certificates for situations that require privacy, but people might not be as concerned about. For example:
Username and password forms
Collecting personal (non-financial) information
On forms where the only users are people who know and trust you
What it comes down to is trust. When you use a self-signed certificate, you are saying to your customers "trust me - I am who I say I am." When you use a certificate signed by a CA, you are saying, "Trust me - Verisign agrees I am who I say I am."
If You're Doing Ecommerce You Need a Signed Certificate
While it is possible your customers will forgive you a self-signed certificate if all they use it for is to login to your website. But if you're asking them to input their credit card or Paypal information, then you really need a signed certificate. Most people trust the signed certificates and won't do business over an HTTPS server without one. So if you're trying to sell something on your website, invest in that certificate. It's just a cost of doing business.
