Let's talk about the 'stamps' & the postage due marking separately:
The 'stamps' are cinderellas. They were not issued by the postal authority/government - they were issued to raise money as a 'charity' venture. So they were never valid as postage stamps.
When something was mailed without sufficient postage, that 'T' marking was used to indicate that there was 'postage due' - it is a substitute for a postage due stamp.
Later, those stamps were overprinted for postal use. You can see an example of this overprint in Turkey in Asia section of Scott catalog; in the link perf12 posted; or on pg 57 & later of this thread:
https://goscf.com/t/50933&whichpage...val%2CleagueSo back to your stamps: we have the naval league labels - without the Turkey in Asia overprint - but with a postage due marking on them. Which obviously makes little sense.
I like your explanation Nigel! And completely agree with you - It seems highly likely - someone was having fun!
My old & not new & fancy Isfila makes no mention of these postage due markings. The naval labels are discussed thoroughly in the other thread...
This is a good link showing the various versions of the postage due stamp & the locations etc:
https://www.turkishpostalhistory.co...om-notes-iii