Jay Conrad Levinson, Jeannie Levinson (2007). “Startup Guide to Guerrilla Marketing: A Simple Battle Plan for First-Time Marketers”, p.53, Entrepreneur Press
"Smarter Branding Without Breaking the Bank: Five Proven Marketing Strategies You Can Use Right Now to Build Your Business at Little Or No Cost". Book by Brenda Bence (p. 91), November 7, 2011.