If the advertiser is geo-targeting the location of where you are searching for, then the fourth line may show the location. As I explained at BrandVerity Blog on this. This seems to be a new behavior from Yahoo, but yes, Google has been doing this for a while.
Here are Google ads for plumbers:
Forum discussion at Sphinn.
Update: Yahoo has sent me a statement:
Yahoo! started labeling the location of ads last just week with the roll out of a new “geo labels” feature. The labeling is displayed primarily for localized queries, like restaurants, florists, mechanics, etc. and is based on the advertiser’s geo targeting preferences and the user’s location of interest.