This finely-cut silver brooch in the form of a sultan’s monogram (tugra) dates to the late 19th century, and was designed to be worn on a coat or a hat. Possibly it was a presentation gift from the court.
Each Ottoman sultan had his own tugra but it is often difficult to tell them apart, so it is difficult to be precise about which sultan is represented by this tugra, but it is likely to be that for Sultan Abdulaziz who ruled the Ottoman empire from 1861 to 1876.
Tugra emblems were worn as brooches occasionally. See Koc (2007, p. 117) for an example set with diamonds.
The example here is in a fine, wearable condition.
References
Koc, A., et al, Istanbul: The City and the Sultan, Nieuwe Kerk, 2007.
Kurkman, G., Ottoman Silver Marks, Mathusalem Publications, 1996.