Hi Jerry,
The initials UL stands for Underwriters Laboratories, a company that is in the business of testing electrical equipment and will certify an equipment line to be safe according to their standards.

They are hired by manufacturers so their products can be UL certified, thereby  instilling trust in the consumer. 

See their web page, geared toward large companies:

http://www.ul.com/global/eng/pages/ 
Cheers,
Laura
Laura Kozuch, Ph.D.
Curator, Illinois State Archaeological Survey
University of Illinois
209 Nuclear Physics
23 Stadium Dr.
Champaign, IL  61820

217-333-0263
FAX  217-244-7458

http://www.isas.uiuc.edu/

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