Please post an image of the rear of the stamp,
I'd like to see the PERFIN
This is a Turkish General Revenue Stamp, 5 Piastres
We both have an unlisted colour variety "Violet Blue"
McDonald lists only Reddish Violet
Correction: My 1 Piastre is listed in Violet Blue, your 5pi is not listed in that colour.
Perf 10.5, 12, 12x13.25, 13.25, 13.25x12,
22.5 x 29.5mm
McDonald Page 22.
24 Revenues listed in set. 10 paras to 90 Piastres.