I can't tell from the image if this stamp's paper is slightly greenish or not. It could be one of 2 "Postal Tax Due" stamps used between 1922-25 and 1923-26 mostly to raise money for the National Fund for Aviation. [If green paper the Scott # would be RAJ15 - if not RAJ19.] "Postal Tax Due" stamps like this one were affixed to mail after mailing when the tax was not required to be paid by the sender. Romania's Postal Tax Stamps and Postal Tax Due Stamps originated in 1915 as a way to fund assistance to the families of soldiers. These stamps in values higher than the mail rates (5 bani - 25 bani) were used to pay taxes on things like on railway and theater tickets.
Hey great info. i dont see the paper green, it seems kind of cream but i am no expert. it says assistenta sociala which i believe is social assistance so i believe it could have been used to pay taxes on other things like you mentioned. thanks