Manuscript "OB" or "O.B." in black, red or blue on 1899 - 1904 issues after the stamps have been affixed to the cover to denote official correspondence. Done in compliance to an  Executive Order issued on December 16, 1905  by C.M. Cotterman, Director of Posts, pertinent details as follows: “An Executive Order issued this date provides that, commencing with January 1st, 1906, all official mail of the insular, provincial and municipal governments, must be fully prepaid by the sending office or official..... Officers purchasing stamps for government business may, if they so desire, surcharge them with the letters “O.B.” either in writing...or by rubber stamp...”

Black "OB" on 3c Jackson

Blue "OB"
on 1c Franklin

Red "OB" on 1c Franklin Strip of 3

3 JANUARY 1906: CEBU to MANILA
Philippine Constabulary official mail with 2c Washington carmine issue of 1903
with black manuscript OB. Backstamped MANILA / JAN 8.

THE EARLIEST RECORDED USE OF MANUSCRIPT "OB"
Frame 1 / Page 4
<Stamping Method
P-4
P-5
P-6
P-7
P-8
Type I Small O.B.>