you can use a custom signature into your Gmail, it's quite easy and simple. just follow the simple steps below:
1- Log in to your Gmail account then go to setting at the top right corner.
2- Now scroll down your muse and look for the option "Signature".
3- Now write your signature that you want to add Ex. (Regards) YOUR SITE NAME etc.
4- Now to add social icons into signature click on the ''Insert image option''
5- Now select the image and click the "link" option and copy and paste your Facebook, Twitter, and any other social network profile or page URL, for Facebook page your URL will look like this https://www.facebook.com/pages/It-Makes-Computing-easy/294662050580520
Now save your setting go to compose a new mail then you see your signature with social networking icons see below.
You can also check it just by sending Emails to your own address.
Must Read: How To Add Social Network Icons Into Rediff mail Signature.