If your Gmail signature isn't displaying properly, you probably need to disable the "Plain Text" mode.
Here are the simple steps to resolve the issue:
Example of the problem:
Instead of :
Solution:
This is probably due to "Plain text" to activate, to deactivate it go to "new message".
You will need to uncheck the "Plain text mode" option and send a new e-mail.
Your signature should be back to normal.