What is another for a tramp stamp?

A tramp steamer of the Liberty or Victory type appears on the Merchant Marine commemorative issued shortly after the war. ( WW2) it is a flush deck, not the more celebrated Three-Island Type with forecastle, mid-section ( wheel room and engine compartment) and after deck. This might be called a tramp stamp- a former maritime club member, I never heard this term applied. Freighters of various types appear in the many national stamps of countries.