Philippines Heacock's Overprint

Saw this on the board from 2011 .. Saw this on ebay

thanks for the lead, I will be bidding

Is it something special?

Partime... It could be if this is the only one known from 1929 .

Was this a company security marking (like a perfin or precancel) or something else?

Commercial Philippine postage stamps with commercial overprints look similar to United States precanceled stamps, but unlike
precanceled stamps they are required to go through the regular mail and be canceled. They were in use from 1924 to 1935.
Philippine businesses wishing to use commercially overprinted postage stamps were required to apply to the Philippine Bureau
of Posts in Manila for permission to use postage stamps bearing an overprint by which their postage stamps could be identified in
case of theft or unauthorised use. The Bureau of Posts required full payment for the postage stamps at the time they were ordered
and would then place the order with the Philippine Bureau of Printing. When the printing was completed, the Bureau of Posts
would deliver the overprinted stamps to the customer.
It seems only five businesses in Manila took advantage of using postage stamps with commercial overprints. This may have been
because the Bureau of Posts and Bureau of Printing were also located in Manila. Although, there were two different times when
two businesses purchased postage stamps and applied their initials or name on the postage stamps using a rubber handstamp
until the Bureau of Posts provided them with overprinted postage stamps.
The records for the denomination of stamps purchased by each company and the quantities of each value overprinted, have never
been recorded in the philatelic press, as the Manila Post Office and all their records were destroyed during World War II.
By 1935, the H. E. Heacock company was the only Philippine business continuing to use postage stamps with commercial
overprints. In October 1935, this company received an order from the Philippine Bureau of Posts prohibiting further use of the
overprinted stamps, and demanded the return of all remaining stamps bearing the overprint; thus ending the use of commercial
overprints.

thanks for the detailed story