Here's your uniform. If the link doesn't work, go to library of congress-prints and photograph division. It is item 234 if you put in WWI as a search, but its direct title and call number are:

True Sons of Freedom (poster)

CALL NUMBER: POS - WWI - US, no. 162 (C size) [P&P]

REPRODUCTION NUMBER: LC-USZC4-2426 (color film copy transparency)
LC-USZ62-117094 (b&w film copy neg.)

I tried to c and p the print, but had no luck. As you probably already know, and one response has told you, it's definitely WWI. S/A collars turned down, at least in everything I've seen, and the general style was less tailored-more related to the older uniforms.