Bosun's whistle, call by H & T ( Hilliard & Thomason ) Birmingham, 1877 , fully hallmarked on other side.
Hilliard & Thomason were well known as silversmiths in Birmingham , making other types of
whistles as well . 
Some other well known British 19th century makers of Bosun's call were Joseph Willmore , George Unite,
Mary Chawner and  E & E Emmanuel to name a few. 
Whistle museum . All rights reserved.

To see and hear lookat  reccomended external links for more info .

*  "The Botswain's Call handbook". The Marine Society & Sea Cadets. http://www.sccheadquarters.com/UserData/root/Files/Training/Proficiencies/Piping/Boatswains%20Call%20Handbook.pdf.  
 *    Listen; MP3s of the Boatswain's call from Hellenic Navy (Greek) 
 *         U.S.A Navy ;How to use Boatswain pipe .pdf file
*               Wikipedia http://en.wikipedia.org/wiki/Bosun's_whistle