Wiktionary
service mark
n. (context legal English) A trademark denoting the source of a service rather than a product.
Wikipedia
Service mark
A service mark or servicemark is a trademark used in the United States and several other countries to identify a service rather than a product. When a service mark is federally registered, the standard registration symbol ® or "Reg U.S. Pat & TM Off" may be used (the same symbol is used to mark registered trademarks). Before it is registered, it is common practice (with some legal standing) to use the service mark symbol ℠ (a superscript SM).