Australian Cover With ?? Backstamp

I have a 1959 Australian cover, but my question is about the interesting X's on the back of the cover. Does anyone know what these were, or were they meaningless? Can someone help? Thanks - Jeff

From the height and position of the markings on the back, I'd suspect ink on the rollers that transported the cover through the cancelling machine at Hobart.

I agree with Tony,
I ran across a similar mutilated square
with an inverted image of a CDS of NZ,
Perhaps the inker continued after a miss
with the previous cover, and you get an "offset" type
impression on the back of the next cover? just guessing.

Hmmmm --- thinking-

X ?
My immediate impression on looking at the back cancellation was that these were aeroplanes, not an X. RAAF is mentioned on the slogan on the front, and the back looked like the rest of the cancellation (in reverse).
A quick search found the whole cancellation on the front of a cover:

http://www.stampboards.com/viewtopi...3947&start=0

That would explain the RE on the backstrike that would finish the slogan "The service with a future" twice. Now for the partial blue strike that does not line up with the rest. Would that be from another cancelling machine, I suppose?

Nice research there 22 crows.

I don't know what type of canceling machines were used but here is an example from U.S.




The offsets on the back were transferred from the previous cover(s)


The letters are placed on the feed tray to the right. The feed rollers pull the letter into the canceller. Once the letters exit on the left they are "fanned out" kind of like a pushed over deck of cards. as the letters continue through the machine the previously canceled letters are pushed to the rack at the left. As the letters overlap they can get an offset image from the letter under it. The is more pronounced and prevalent if the canceler is overinking.