Linkman used the spade logo on several different lines of pipes before it was used on the Dr. Grabow. In 1944 the Dr. Grabow Pipe Co. was formed as an off shoot or subsidiary owned by Linkman as I understand it.All my linkman's have the propeller symbol, not sure when they switched to the spade
Dr. Grabows made after 1944 are not stamped Linkman and that may be when they started being made with the spade emblem.
This is from an article written by Dr. D.R. Bridges and posted on RJ McKay's website-- http://drgrabow-pipe-info.com/
The Dr. Grabow pipe was only one of several pipe brands made at the Linkman plant on W. Fullerton Ave., but they must have earned the public’s approval, because a 1937 Linkman publication shows sales of their Dr. Grabow pipes increased by approximately 8-fold in their first six years.
Dr. Grabow pipe sales continued to increase and in October of 1944, the Dr. Grabow Pipe Co. was formed and incorporated. Its founding incorporators included Richard J. Dean, Angelo Pinasco, and Harry A. Shapiro. The corporate address remained in the M. Linkman building on W. Fullerton. We have found no evidence showing that anyone other than M. Linkman produced the Dr. Grabow pipe for the Dr. Grabow Pipe Co. of Chicago.
In February of 1953, the Dr. Grabow Pipe Co. filed corporate dissolution papers. The next month in March, Henry Leonard and Thomas of Greensboro, North Carolina announced they had acquired the Dr. Grabow and M. Linkman business. The Chicago factory continued to produce Dr. Grabow pipes for a few months until manufacturing equipment could be moved from Chicago to HL&T’s factory, Sparta Pipes, in Sparta, North Carolina. In December of 1953 the Dr. Grabow Pipe Co., corporation of Chicago finally dissolved.