The only known comparable stamp is in the British Museum, acquired in 1880. Both use an alphabet classified as Gilgit/Bamiyan-Typ II, or Proto-Sarada, with a relationship to Northern Gupta Brahmi of the 6th century ad. Both stamps have similar handles and petal decoration on the reverse, and are attributed to the same workshop. Unravelling the exact origin of the text, like the exact type of its alphabet, is a mind-crunching exercise, fascinating to specialists and best left to them.
Published: Prajnadhara: Essays on Asian Art History, Epigraphy and Culture, Gerd J.R. Mevissen and Arundhati Banerji (eds.), New Delhi, 2009, pp. 41–2, pl. 4.3