In the process of researching various test stamps, I fortuitously came across a tiny article in an ancient magazine.*
This little notification positively identifies the full name of Scott #TD63B
, which had been previously only listed as "Security Coil" in the Scott Specialized Catalogue.
The actual name of the company is the Security Sealing and Stamping Machine Company.
Given the length of their company name, it is no wonder that it was shortened to just a stylized "Security" for their test stamp.
This is an extremely rare stamp, with very few copies being known.
Now you know something that, apparently, no one alive today has previously known.
Thought that you'd like that.
, Volume 34, June 22, 1911, page 1,191.