I almost forgot to share with you, one of the most beautiful triangular stamps I have.
For this last item on 'triangular' stamps, I take you to the Baltic region, showing airmail stamps of Estonia, Latvia and Lithuania.
Where african countries use triangular stamps mainly for revenue stamps (tax); the Baltic area has this preference to use triangular stamps for airmail. At least, in a time where airmail stamps were different from regular 'land mail' stamps.
In a way the purpose was the same. One look at the letter could tell you what kind of mail it was.
As revenue stamps draw the attention in Africa, here the airmail stamps will surely have drawn the attention.
A more detailed look will be posted later, when I talk about the Baltic Countries in particular.