Jonathan R. Zatlin. The Currency of Socialism : Money and Political Culture in East Germany, p.245. Cambridge University Press, 2007. ISBN 978-0-521-86956-0 /wiki/ISBN_(identifier)
Everyday Life in Eastern Europe. at the Centre for History and New Media http://chnm.gmu.edu/1989/exhibits/everyday-life/primary-sources/12
Made in Bulgaria: The national as advertising repertoire Archived 2009-03-29 at the Wayback Machine by Milla Mineva at Eurozine http://www.eurozine.com/articles/2008-11-13-mineva-en.html