What is a "UT Test?"

While railfnning today, I found a placard with the word “UT TEST” printed on it along with “Progress Rail Services.” It looks like it fell off a railcar. What exactly is a UT Test?

Most likely “Ultrasonic Testing”. Commonly used to check metal for cracks. See this brief introduction to UT:

http://www.ndt-ed.org/EducationResources/CommunityCollege/Ultrasonics/Introduction/description.htm

Regards

Ed