ransom card

[pars]

Dear all!
What is the exact meaning of "ransom card" the following passage? It is from the book “Persian Gulf Command” by Ashley Jackson, p. 225. It is about a group of British soldiers who were captured by the Iraqi tribesmen in 1941 during the war between the two countries.

[We] noticed some tribesmen standing by and approached with intention of asking if we could use one of their boats. Did not understand and made us go to their village where I offered an Egyptian pound note for use of a boat. Took note but refused boat. I then produced the ‘ransom card’, of which they took no notice. They then suddenly attacked us,
using clubs, sticks, etc. and relieved us of our valuables and disarmed us. All injured to various degrees. Eventually [Iraqi] soldiers arrived and took us to their barracks across the river, then to Baghdad.

Accept my endless tanks.

[PeterCW]

I haven't come across the expression before but I know that military personel did sometimes carry cards written in the local langauge to help identify themselves if stranded. I would guess that in this case payment was promised for helping them return to their base.

[Charlie Bernstein]

. . . Accept my endless tanks.

But where will we put them?

[tzfujimino]

But where will we put them?

Charlie: Shall I put them here?
tzfujimino (with a foreign accent): No, tanks. I don't need no (any) tanks.