These are commonly used internet expressions used to show certain emotions. Instead of explaining how they feel, people will use an expression to represent it. This is also used for emotions that you may feel is something that can only be shown.
:-D This would display happinness.
:( This would display sadness.
:P This would display a number of things.
Prices shown in USD.
邮件由 firstname.lastname@example.org 发出。我们决不会发送垃圾邮件。