Montenegro, 12 July 1902, SG107, but you'll probably want a Scott number - sorry.
The letters on the right that start with what looks like UP (but are in fact 'tsr', short for Tsrna Gora, the 'Black Mountain') always indicate Montenegro.
It is Montenegro (Crna Gora), issue from 1902 year (1/14 July),
Full set have 9 values, and under Michel number (sample You have) is #44 (0.50 euro catalog value).
