Transcaucasian SSR. Cover of registered letter sent from Tiflis (TSSR) on January 3, 1924.

Cover of registered letter sent from Tiflis (TSSR) to Vaucresson (France) on January 3, 1924. Cover paid according to the tax (for International registered letter) - 0,40 k. Cover is franked with 2 stamps of TSSR (total sum - 36 k.) and 2 stamps of USSR (total sum - 4 k.). This mixed franking meets extremely rare. TSSR stamps were withdrawn after addition TSSR to the USSR.
Only two letters with TSSR and USSR stamps (mixed franking) are known at the present time. Very rare.