This is currently a known source of spam, and one of the reasons why in many countries all Map Maker edits must be approved by at least one trusted reviewer before they are being published. Unfortunately the edits you found passed that review without being detected.
There are several methods to report this type of spam. One is what you have already done by reviewing the edit and marking it as spam there.
Another method is to open the profile of the mapper. That profile should be accessible through a link which is available within the edit. If you open that page, you will see a "Report user as spammer" link in the upper left corner.
If this type of spam is happening a lot in your area with different spammers, it is not a bad idea to also inform the reviewers who are active in that area to watch out more. You can do that by finding the Map Maker Advocate who is active in that country or state through http://sites.google.com/site/mapyourworldcommunity/advocates [sites.google.com] and send a message through their Google+ account. They should be able to inform the reviewers who are commonly reviewing in that specific area.