I believe, the term safety switch was coined by Square D to describe the safety provided by their enclosed disconnect switch.
Go to http://www.squared.com/us/squared/corporate_info.nsf/unid/A21F52058A62BF0C85256A4C004CFBA2/$file/histsqdFrameset.htm for Square D's history.
In reality even the term "disconnect switch" is not defined. Disconnects (as a shortening of the term Disconnecting Means) are mentioned in th NEC but not specifically switches.
IMHO, If it is a switch, and it removes conductors from their source, then it is a disconnect switch. If it is also enclosed then it is a safety switch.
The only applicable standards I know of are:
UL98 - Enclosed and Dead Front Switches and
NEMA Standards Publication KS1 - Enclosed Switches
