Lettraset kind of Stencils (rub-on) are a good alternative, but again they'll look brand new. You'll have to do your weathering and all after putting on the transfers (something you should do with decals too, however, the washes and drybrushing can make the carrier film appear, and therefore I would cut my decals as close as possible to the actual design).
A number of companies sell etched stencils sets that allow you to paint (preferably airbrush) numbers, stars, crosses,..). You might consider that a better alternative as it will be easier to get the worn look straight away.
I've posted pictures a couple of times here, but they need to be on the web somewhere first.