1. Murales Bolognese: Visual Representation of Italian Urban Culture;Glăvan;Sociol. Românească,2014
2. Symbols: A Universal Language;Piercy,2013
3. Trains, railroad workers and illegal riders: The subcultural world of hobo graffiti;Lennon,2016
4. Hoboglyphs: Secret Transient Symbols and Modern Nomad Codes
https://weburbanist.com/2010/06/03/hoboglyphs-secret-transient-symbols-modern-nomad-codes/
5. Graffiti New York;Felisbret,2009