The Director of Posts, C.M. Cotterman, in granting the permission wrote a letter to the Director of the Bureau of Printing, dated May 25, 1907, requesting the “...overprint with the letters “O.B.” such unused Philippine postage stamps as may be delivered to you by any government bureau  or  bureaus for such purpose; the cost of this printing to be charged  to the Bureau of Posts...In the first lot it may be advisable to make trials of several colors of ink to determine the most suitable, but it is requested that the letters “O.B.” be uniform throughout, and the selection of type is left to your superior judgment.”

Only the Philippine Constabulary availed of the request made by Mr. Cotterman when the stamp clerk at Constabulary headquarters delivered to the Bureau of Printing all stamps on hand, regardless of the issue or quantity, by making them up into sheets for printing by mounting loose stamps in small quantities as to hold them together. The resulting overprinted stamps are now popularly known as the BANDHOLTZ OVERPRINTS. 

Inasmuch as the overprinting was with Bureau of Posts authority, it is only fitting to consider these stamps as legitimate official stamps. There will always be an argument as to the status of the stamps since Gen. Bandholtz was a noted stamp collector. However it cannot be denied that his request for the experimental overprint was for a valid reason which later resulted in the actual use by the Philippine Constabulary of the 1906 - 1911 Definitives overprinted "OB". At the same time the Philippine Constabulary cannot be faulted for being the only government department that availed of Mr. Cotterman's approval for the experimental overprint. 

The reference numbers I am assigning will be easy to recall: adding to the Scott numbers the prefix "OB" to denote Official Business and the suffix BK, RD, BL, GR and YL to denote the Black, Red, Black, Green and Yellow overprint colors.