Dear Ms. Friederichsen,
Thank you for posting your request on History Hub!
We searched the National Archives Catalog and located a series titled Decimal Files, 1943 - 1944 that included a file unit titled [314.7] 593rd Joint Assault Signal Company  and a series titled Unit Histories, 1943 - 1967 that included a file unit titled Headquarters, 593rd Joint Assault Signal Company: Historical Reports in the Records of U.S. Army Operational, Tactical, and Support Organizations (World War II and Thereafter) (Record Group 338). We also located a series titled World War II Operations Reports, 1940-1948 in the Records of the Adjutant General's Office (Record Group 407) that includes a unit history for 1944 and after action reports for 1944 through 1945 of the 593rd Joint Assault Signal Company (593rd JASCO).
We also located the World War II War Diaries, Other Operational Records and Histories, ca. 1/1/1942 - ca. 6/1/1946 in the Records of the Office of the Chief of Naval Operations (Record Group 38) that includes the “Report of operations in the invasion & occupation of Okinawa Shima, Ryukyu Islands, 4/1/45 to 6/21/45” from the 593rd JASCO. This report has been digitized and can be viewed through Fold3. There may be a fee for this service. Instead, you may view these records online at one of NARA's facilities for free via a NARA PC. For the nearest NARA location, please consult our web page at http://www.archives.gov/locations/. Additionally, you may check with your local public or university library as these institutions sometimes provide access to Fold3.
For access to and/or copies of the records in Record Group 338, 407 and Record Group 38, please contact the National Archives at College Park - Textual Reference (RDT2) via email at email@example.com.
We also searched the Ike Skelton Combined Arms Research Library and located several documents relating to the 593rd JASCO which have been digitized and can be viewed through their Digital Library.
In addition, we searched online and located the following sources mentioning the 593rd JASCO.
We hope this information is helpful. Best of luck with your family research!