The Civil War Relicman, Harry Ridgeway
	Winchester, Virginia  Civil War buttons bought and sold
	relicman.com

Ridgeway Reference Archive, Civil War buttons
Catalog of button backmarks 
Guiterman & Bro. Ann Arbor Michigan

Guiterman & Bro is clearly a custom retailer supplying the University of Michigan in Ann Arbor Michigan.  This maker is not listed in Tice or Bazelon, so at this point not much is known.  The University of Michigan button does employ a definite Scovill die for the motif, and the back is of the same style as other Scovill backs dating to around 1860.

Most information on this page is from Tice's book, Dating Buttons..., the pictures are generally from buttons that I have handled. 

Guiterman01, (24mm)

Backmark:  "GUITERMAN & BRO. / ANN ARBOR, MICH." dm two solid inner rings, unknown maker backmark appears to be Scovill manufacture, (Guiterman01). 
Tice, not listed.

B5030       Michigan school button, "University of Michigan" with state seal elk and moose, officer staff style, Guiterman & Bro Ann Arbor Mich. dm, ( 23.6mm)