Now this is a new usage to me - I've never heard it used this side of the slop-bowl. Over here, the only slang use I know of is in the theatre, where "props" are the bits and pieces that an actor usesd on stage, other than actual furniture: glasses, bottles, candlesticks, daggers and swords, knives forks and plates - all that sort of thing.

In that context, it is an abbrev. of "stage properties."