Gmail does not support rich text signature. That means you can’t have link, colors, images or any formatting with the Gmail signature.
There are ways to get around it.
1. copy and paste
Make your signature in Word and copy it to gmail’s composer each time you want to send an email.
2. Chrome/Firefox extension.
The extension allows you to save your signature in your browser.
But if you use another PC, you will not be able to have the signature coming up automatically because it is saved to the PC where you installed the extension.