From Google Adsense at https://support.google.com/adsense/answer/4533986?hl=en
Labeling ads
Publishers have two options for how to label AdSense ad units: You can either label the units with "Advertisements" or "Sponsored Links". No other variations are allowed at this time.
How do I create CSS for this?
This solution works for me. Does anyone see a problem or offer a better solution?
For horizontal ads, wrap your ad with a div
<div class="adHorizontal">
And use this CSS:
div.adHorizontal ins.adsbygoogle:before {
content: 'Advertisement';
position: relative;
top: 15px;
color: #888;
font-size: .75rem;
-webkit-transform: rotate(270deg);
transform: rotate(270deg);
transform-origin: right top 0;
float:right;}