Green’s Dictionary of Slang

(US tramp) the false door at the end of carriages; thus places between the carriages where a tramp can hide while riding on a passenger train.

1929		E. Booth Stealing Through Life 7: On the trains we saw no ‘blinds,’ no ‘trucks,’ no steps by which we could climb to the car tops.
1930		G. Milburn ‘A Hard Road to Ride’ in Hobo’s Hornbook 247: So I’m on the blinds of the Flying Crow / And I’m going to ride her through.
1960		(con. 1950-1960) R.A. Freeman Dict. Inmate Sl. (Walla Walla, WA) 12: Blinds – the false doors at the ends of a baggage car.