The following custom styles utilize the official alternate logo, which you are free to use.
Alternate Logo #1 (Same Text as Main Logo)
Alternate Logo #2 (Modified Digital Text)
Alternate Logo #3 (No Text)
To install all you need to do is install Stylsh, click the link with the corresponding theme, and finally click the Install to Stylish button. If you want to change themes, all you need to do is press the disable button when you click the Stylish button in the top right of the screen.
Stylish for Mozilla: https://addons.mozilla.org/en-US/firefox/addon/stylish/
Stylish for Chrome: https://chrome.google.com/webstore/detail/stylish/fjnbnpbmkenffdnngjfgmeleoegfcffe?hl=en
Stylish for Safari: http://sobolev.us/stylish/