Here is (possibly) the earliest mention found so far of Will Jackman in a baseball context.  In 1922 a semi-pro team called the St. Louis Tigers took over the grounds formerly occupied by the St. Louis Giants, and, led by their manager, W.C. Wiley of Galveston, Texas, imported a bunch of players from the Texas Colored League and elsewhere.  “William Jackman, Houston, p,” appears in the tenth line from the bottom.  (Apologies for the faint image.)

(St. Louis Argus, April 14, 1922, p. 10)

There a few other players of note here, such as Thomas Gee (brother of Richard Gee), who would later catch for the Lincoln Giants and Newark Stars of the Eastern Colored League, and James “Baby” or “Babe” White, who I believe appeared briefly for the St. Louis Stars later in 1922.  As far as I can tell, Jackman didn’t stick with the team for long.

Anyway, I wish Dick Thompson were around so I could ask him about it.

As always, thanks to Patrick Rock for the great material from the St. Louis Argus.

UPDATE 2/9/2009 Per Bijan Bayne’s request in comments, here are the players for the St. Louis Tigers, as listed in the article above:

“Jas. “Baby” White, formerly with Beaumont Oilers, 2b; Elisha Warren, Galveston Sand Crabs, 3b; William Hines, Houston Buffaloes, 1b; Robert Davis, All Nations, p; Chas. Hunter, Beaumont, outfield; William Jackman, Houston, p; Lawson Perry, ss; Thomas Calloway and Lloyd Evans, outfield, all from Houston; Thos. Gee, c, and Curtis Boyce, p, from the Galveston Sand Crabs.”