what was a signal company’s function in WWII?

In my father’s New Testament carried in WWII, he wrote: 3rd signal company, 29th service group, then his name, service # and social. At ancestry.com I discovered a little more info from U.S. World War II Army enlistment Records, but these items I do not understand: under branch, it says “branch immaterial-warrant officers, USA” & same thing under branch code. Under component, it says “Selectees (enlisted men).” Under term of enlistment it says: “Enlistment for Phillipine department” but dad only served in Europe. How I know this: I discovered that the 3rd signal company was in the 3rd infantry, so they were only in Europe. Dad went in at Fort McPherson, Atlanta, HQ, Third U.S. Army. (Patton’s Army in part of WWII). Can anyone help me understand what the 3rd signal company was and what type of jobs they did so I can understand what dad did in the War? What is a service group? Thanks in advance!!

LACEY