For Worldwide Collectors (Long may they endure)
The tricky stamps / Labels one comes across in stamp boxes.
Canadian War tax Embossed Impressed Duty stamp, Inland Revenue, Beaver.
Not in Barefoot, Van Dam, wiki, and eBay
A favourite tricky
Bahrain War tax
I was lucky with Pmk as AMMAN led me to Jordan
Similar Script searches, may help searching
Libya, Cyrenacia, Saudia Arabia, Syria, Jordan, Bahrain, Egypt, Hejaz.