Saldus is the Latvian name. In the postmark below you see that the Russian name more a transscription is of the German name Frauenburg: ФРУЕНБУРГЪ (FRAUENBURG).
The postmark is a double circle postmark. In the classification of the EESTI-classification type 7.
In the postmark is also indicated КУРЛ Г. (KURL G.), short for КУРЛЯНДСКАЯ (KURLYANDSKAYA) ГУБЕРНIЯ (GUBERNIYA), Courland Government, so this is type 7A (with gubernia).
In the subdivision: 7A1: * * a etc.
Detail of the map [Wereld-Atlas voor Kantoor en Huiskamer / door J. Kuyper. – 1e Deel Europa. – Amsterdan : G.L. Funke, 1880] : the German name is used: Frauenburg.